Method of making ceramic aggregate particles

ABSTRACT

Methods for making ceramic aggregate particles comprising forming a plurality of ceramic aggregate precursor particles from a composition by forcing the composition through at least one orifice in a substrate, at least partially curing the ceramic aggregate precursor particles, and heating the ceramic aggregate precursor particles to provide ceramic aggregate particles wherein solid particulates are bonded together by ceramic binder. In another aspect, the present invention provides methods for making an abrasive article utilizing methods for making abrasive ceramic aggregate particles comprising forming a plurality of ceramic aggregate precursor particles by passing a composition through at least one orifice in a substrate, separating the abrasive ceramic aggregate precursor particles from the substrate, at least partially curing the abrasive ceramic aggregate precursor particles, heating the abrasive ceramic aggregate precursor particles to provide abrasive ceramic aggregate particles bonded together by ceramic binder, and combining at least a portion of the abrasive ceramic aggregate particles with abrasive article binder material and abrasive material, with or without another abrasive material, to provide an abrasive article.

This application is a continuation-in-part of the U.S. patentapplications having U.S. Ser. Nos. 09/688,444, 09/688,484, and09/688,486 filed Oct. 16, 2000, the disclosures of which areincorporated by reference.

FIELD OF THE INVENTION

The present invention relates to methods of making ceramic aggregateparticles. More particularly, the present invention relates to methodsof making ceramic aggregate particles comprising ceramic binder, and aplurality of solid particulates. The solid particulates may be abrasiveparticulates.

BACKGROUND

A variety of methods of making ceramic aggregate particles, for use in avariety of industries, exist. For example, catalyst pellets used in thehydrogenation of toluene and heptane can be made by combining a metalalloy, a high molecular weight polymer, and optionally a plasticizer(i.e., a transient solvent) into a mixture, forming the mixture into ashape, extracting the plasticizer (e.g., by solvent extraction),calcining the shaped mixture to remove the polymer, and then sinteringthe shaped mixture to provide catalyst pellets. Additional informationcan be found in U.S. Pat. Nos. 4,895,994 (Cheng et al.) and 4,900,698(Lundsager). In the orthopedic and dental industry, hard, shaped,ceramic bodies can be made by melting ceramic binder precursor, coolingthe melt, and then crushing the cooled melt to provide ceramic bodies tobe used in synthetic bone and dental composition. Additional informationcan be found in U.S. Pat. No. 5,914,356 (Erbe). In the abrasivesindustry, ceramic aggregate particles can be made by forming acomposition that includes a ceramic binder precursor and a temporaryorganic binder precursor, placing the composition into a mold, heatingthe composition in the mold to provide shaped particles, and sinteringthe shaped particles to bum off the organic binder and provide ceramicaggregate particles. Additional information can be found in U.S. Pat.No. 5,975,988 (Christianson). Other uses for ceramic aggregate particlesinclude, for example, roofing granules, filtration products, hardcoatings, shot blast media, tumbling media, brake linings, anti-slip andwear resistant coatings, retro-reflective sheeting and laminatecomposite structures.

While these conventional techniques are useful, there is always a needfor other useful techniques which are less costly, require less labor,require less process space, or require fewer steps than conventionaltechniques, or, that provide ceramic aggregate particles having similaror improved properties over those made by conventional techniques. Forexample, techniques for forming ceramic aggregate particles which do notrequire a molding step may provide a less expensive process.Additionally, techniques which do not require the use of solvents (e.g.,toluene or heptane) may be desirable.

A need also exists for a method to produce ceramic aggregate particleswhich have relatively consistent shapes and sizes in order to providegreater consistency of performance to articles made with such ceramicaggregate particles. Regarding particularly abrasive articles, forexample, there continues to be a need for abrasive particles which canprovide abrasive surfaces with sustained consistent cut rates for,preferably, extended life times, with consistent work piece finish.

SUMMARY OF THE INVENTION

The present invention provides methods of making ceramic aggregateparticles. One method according to the present invention comprises:

forming a plurality of ceramic aggregate precursor particles from acomposition comprising curable binder precursor material, and ceramicbinder precursor material, and a plurality of solid particulates, byforcing the composition through a perforated substrate;

at least partially curing the ceramic aggregate precursor particles;

separating the aggregate precursor particles from the perforatedsubstrate; and

heating the ceramic aggregate precursor particles to provide ceramicaggregate particles, wherein the solid particulates are bonded togetherby the ceramic binder

In one aspect, the present invention may further comprise the step ofcombining at least a portion of the ceramic aggregate particles withabrasive article binder material and abrasive material to provide anabrasive article. Alternatively, at least a portion of the ceramicaggregate particles comprise abrasive particles.

Typically, the composition is essentially free of solvent. In oneembodiment of methods according to the present invention, the mixture ofcomponents may further comprise a plurality of solid particulates. Theplurality of solid particulates typically have an average particle sizein the range from about 0.5 micrometers to about 1500 micrometers.Typically, the mixture of components further comprises photoinitiator.In one embodiment, the at least partially curing step may comprisethermal curing, radiation curing, or combinations thereof. During theheating step, heating is typically conducted at a temperature in therange from about 500° C. to about 1500° C.

As used herein, the expression “curable binder precursor material”refers to any material that is deformable or can be made to be deformedby heat or pressure or both and can be at least partially cured toprovide material, such as, for example, ceramic aggregate precursorparticles, that are handleable and collectable. As used herein withrespect to curable binder precursor material, the expression “at leastpartially cured” means “part” or “all” of the curable binder precursormaterial has been cured to such a degree that it is handleable andcollectable. The expression “at least partially cured” does not meanthat part or all of the curable binder precursor is always fully cured,but that it is sufficiently cured, after being at least partially cured,to be handleable and collectable.

As used herein, the expression “handleable and collectable” refers tomaterial that will not substantially flow or experience a substantialchange in shape. Ceramic aggregate precursor particles and ceramicaggregate particles that are handleable and collectable tend to remainintact if subjected to an applied force that tends to strain or deform abody. Ceramic aggregate precursor particles and ceramic aggregateparticles that are not handleable and collectable tend not to remainintact if subjected to an applied force that tends to strain or deform abody.

As used herein, the expression “ceramic binder precursor material”refers to particulate additives which, when heated to a temperaturesufficient to bum out organic materials present in the ceramic aggregateprecursor particle, may subsequently bond together to form a rigidceramic phase bonding the ceramic aggregate particle together and toprovide a ceramic aggregate particle. Ceramic binder precursor materialmay include crystalline or non-crystalline ceramic material.Hereinafter, “ceramic aggregate precursor particle” means the ceramicbinder precursor material has not yet bonded together sufficiently toprovide a particle that is handleable and collectable. Hereinafter,“ceramic aggregate particle” means the ceramic binder precursor materialhas sufficiently bonded together to provide a particle that ishandleable and collectable. Typically, methods according to the presentinvention provide at least a portion of the ceramic aggregate particleshaving an aspect ratio greater than one.

As used herein, the word “ceramic” means inorganic, non-metallicmaterial that may include a crystalline phase, a noncrystalline phase(e.g., glass), or a combination of both a crystalline phase and anon-crystalline phase (e.g., porcelain, glass-ceramic).

Hereinafter, “essentially free of solvents” means the composition usedto make ceramic aggregate precursor particles contains less than 10%solvent.

Ceramic aggregate particles made by the present invention can be used inproducts such as, for example, abrasives, roofing granules, filtrationproducts, hard coatings, shot blast media, tumbling media, brakelinings, anti-slip and wear resistant coatings, synthetic bone, dentalcompositions, retro-reflective sheeting and laminate compositestructures.

In one embodiment, methods according to the present invention involvecombining at least a portion of the cured ceramic aggregate particleswith abrasive article binder material and abrasive material to providean abrasive article. Suitable abrasive articles include coated abrasivearticles (including nonwoven abrasive articles) and bonded abrasivearticles.

The method of the present invention provides ceramic aggregate particleswhere a major portion of the particles have a substantially uniformcross-sectional shape. By “major portion” it is meant that at least 50percent, preferably about 90 percent, of the particles have asubstantially uniform cross-sectional shape. Such uniform particlesprovide articles into which they are incorporated with more consistentperformance characteristics. For example, abrasive ceramic aggregatemade according to the present invention have consistently high cut ratesand consistent surface finish for longer life times than do abrasiveaggregates prepared by conventional methods.

The method of forming the aggregates of the invention described aboveare generally less costly, and require fewer steps, and less space andlabor than conventional means of making ceramic aggregate particles,such as molding.

The ceramic aggregates produced by the methods of this invention aredescribed in Applicant's U.S. Ser. No. 09/971,899 (filed on the samedate as this application and incorporated herein).

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic side view in elevation of an exemplary ceramicaggregate particle made according to a method of the present invention.

FIG. 2 is a printed, digitized image of an exemplary ceramic aggregateparticle made according to a method of the present invention.

FIG. 3 is a schematic side view illustrating a device for practicing amethod of the present invention.

FIG. 4 is a perspective view of a portion of a device for practicing amethod of the present invention, with a front portion of the device cutaway to expose a portion of the interior of the device.

FIG. 5 is a perspective view of a portion of the screen used in thedevice shown in FIG. 4.

FIG. 6 is a fragmentary cross-sectional schematic view of a coatedabrasive article including abrasive ceramic aggregate particlesaccording to the present invention.

FIG. 7 is a perspective view of a bonded abrasive article includingabrasive ceramic aggregate particles according to the present invention.

FIG. 8 is an enlarged schematic view of a nonwoven abrasive articleincluding abrasive ceramic aggregate particles according to the presentinvention.

DESCRIPTION

In one embodiment, a method according to the present invention utilizesa composition comprising a mixture of components comprising curablebinder precursor material, ceramic binder precursor material, and aplurality of solid particulates to make ceramic aggregate precursorparticles. Optionally an initiator and/or other modifying additives maybe included in the mixture. In one embodiment at least a portion of thesolid particulates are abrasive grits or particles.

Curable Binder Precursor

Curable binder precursor can be cured by radiation energy or thermalenergy. Typically, radiation curable binder precursor material comprisesat least one of epoxy resin, acrylated urethane resin, acrylated epoxyresin, ethylenically unsaturated resin, aminoplast resin having at leastone pendant unsaturated carbonyl group, isocyanurate derivatives havingat least one pendant acrylate group, isocyanate derivatives having atleast one pendant acrylate group, or combinations thereof. Other usefulradiation curable binder precursor material includes vinyl ethers.

Epoxies have an oxirane ring and are polymerized by the ring opening viaa cationic mechanism. Useful epoxy resins include monomeric epoxy resinsand polymeric epoxy resins. These resins can vary greatly in the natureof their backbones and substituent groups. For example, the backbone maybe of any type normally associated with epoxy resins and substituentgroups thereon can be any group free of an active hydrogen atom that isreactive with an oxirane ring at room temperature. Representativeexamples of substituent groups for epoxy resins include halogens, estergroups, ether groups, sulfonate groups, siloxane groups, nitro groups,and phosphate groups. Examples of some epoxy resins useful in thisinvention include 2,2-bis[4-(2,3-epoxypropyloxy)phenyl]propane(diglycidyl ether of bisphenol A) and materials under the tradedesignation “EPON 828”, “EPON 1004” and “EPON 1001F”, commerciallyavailable from Shell Chemical Co., Houston, Tex., “DER-331”, “DER-332”and “DER-334”, commercially available from Dow Chemical Co., Freeport,Tex., Other suitable epoxy resins include glycidyl ethers of phenolformaldehyde novolac (e.g., “DEN-431” and “DEN-428”, commerciallyavailable from Dow Chemical Co.). The epoxy resins used in the inventioncan polymerize via a cationic mechanism with the addition of appropriatephotoinitiator(s). These resins are further described in U.S. Pat. Nos.4,318,766 and 4,751,138, which are incorporated by reference.

Exemplary acrylated urethane resin includes a diacrylate ester of ahydroxy terminated isocyanate extended polyester or polyether. Examplesof commercially available acrylated urethane resin include “UVITHANE782” and “UVITHANE 783,” both available from Morton Thiokol Chemical,Moss Point, Miss., and “CMD 6600”, “CMD 8400”, and “CMD 8805”, allavailable from Radcure Specialties, Pampa, Tex.

Exemplary acrylated epoxy resin includes a diacrylate ester of epoxyresin, such as the diacrylate ester of an epoxy resin such as bisphenol.Examples of commercially available acrylated epoxy resin include “CMD3500”, “CMD 3600”, and “CMD 3700”, available from Radcure Specialties.

Exemplary ethylenically unsaturated resin includes both monomeric andpolymeric compounds that contain atoms of carbon, hydrogen and oxygen,and optionally, nitrogen or the halogens. Oxygen atoms, nitrogen atoms,or both, are generally present in ether, ester, urethane, amide, andurea groups. Ethylenically unsaturated resin typically has a molecularweight of less than about 4,000 and is in one embodiment an esterresulting from the reaction of compounds containing aliphaticmonohydroxy groups or aliphatic polyhydroxy groups and unsaturatedcarboxylic acids, such as acrylic acid, methacrylic acid, itaconic acid,crotonic acid, isocrotonic acid, maleic acid, and the like.

Representative examples of other useful acrylates include methylmethacrylate, ethyl methacrylate, ethylene glycol diacrylate, ethyleneglycol methacrylate, hexanediol diacrylate, triethylene glycoldiacrylate, trimethylolpropane triacrylate, glycerol triacrylate,pentaerythritol triacrylate, pentaerythritol methacrylate, andpentaerythritol tetraacrylate. Other useful ethylenically unsaturatedresins include monoallyl, polyallyl, and polymethylallyl esters andamides of carboxylic acids, such as diallyl phthalate, diallyl adipate,and N,N-diallyladipamide. Still, other useful ethylenically unsaturatedresins include styrene, divinyl benzene, and vinyl toluene. Other usefulnitrogen-containing, ethylenically unsaturated resins includetris(2-acryloyl-oxyethyl)isocyanurate,1,3,5-tri(2-methyacryloxyethyl)-s-triazine, acrylamide,methylacrylamide, N-methylacrylamide, N,N-dimethylacrylamide,N-vinylpyrrolidone, and N-vinylpiperidone.

Some useful aminoplast resins can be monomeric or oligomeric. Typically,the aminoplast resins have at least one pendant a,-unsaturated carbonylgroup per molecule. These α,β-unsaturated carbonyl groups can beacrylate, methacrylate, or acrylamide groups. Examples of such resinsinclude N-hydroxymethyl-acrylamide, N,N′-oxydimethylenebisacrylamide,ortho and para acrylamidomethylated phenol, acrylamidomethylatedphenolic novolac, and combinations thereof. These materials are furtherdescribed in U.S. Pat. Nos. 4,903,440 and 5,236,472, which areincorporated by reference.

Useful isocyanurate derivatives having at least one pendant acrylategroup and isocyanate derivatives having at least one pendant acrylategroup are further described in U.S. Pat. No. 4,652,274, which isincorporated by reference. One such isocyanurate material is atriacrylate of tris(2-hydroxyethyl)isocyanurate.

Examples of vinyl ethers suitable for this invention include vinyl etherfunctionalized urethane oligomers, commercially available from AlliedSignal, Morristown, N.J., under the trade designations “VE 4010”, “VE4015”, “VE 2010”, “VE 2020”, and “VE 4020”.

Ceramic Binder Precursor

Ceramic binder precursor includes crystalline and/or non-crystallineceramic materials which are non-foaming. Typically, ceramic binderprecursor material is selected from the group consisting of glasspowder, frits, clay, fluxing minerals, silica sols, sinterable ceramicpowders or combinations thereof. After heating, the ceramic binderprecursor material forms ceramic binder. Typically, utilizing a methodof the present invention, the ceramic binder bonds solid particulates,such as abrasive grains, together to form ceramic aggregate particles.

Useful glass powder may include silicate or non-silicate based glasspowder. Silicate based glass powder may be single-phase ormulti-component systems. In one embodiment, a single-phase glass powderincludes vitreous silica. Multi-component silicate glass powdertypically contains modifiers or intermediates, such as, for example,metal oxides. Useful examples of multi-component silicate glass powderinclude alkali silicates, containing alkali metal oxides; soda-limeglasses, containing alkali and alkaline earth metal oxides, plus,typically, small amounts of alumina and other miscellaneous oxides;borosilicate glasses; aluminosilicate glasses; lead glasses. Usefulnon-silicate based glass powder may include vitreous metal and non-metaloxide systems, including, but not limited to, P₂O₅, GeO₂, B₂O₃, Al₂O₃,Li₂O, Na₂O, K₂O, BeO, MgO, CaO, BaO, PbO, ZnO and FeO. Other usefulexamples of non-silicate glasses include borate glasses, such asLindemann glasses (Li₂O.BeO. B₂O₃); phosphate glasses; calcium aluminateglasses; calcium germanate glasses.

By definition, glass-ceramics are at least 50% crystalline. Examples ofcrystalline phases include β-quartz; β-quartz solid solution;β-spodumene solid solution, Li₂O.Al₂O₃.(SiO₂)₄₋₁₀; lithiummetasilicate-lithium disilicate, Li₂O.SiO₂-Li₂O.2SiO₂;β-spodumene solidsolution-mullite, Li₂O.Al₂O₃.(SiO₂)₄₋₁₀-3Al₂O₃.2SiO₂; α-quartz solisolution-spinel-enstatite, SiO₂—MgO.Al₂O₃—MgO.SiO₂. Titanate orzirconates are typically employed as the primary crystalline nuclei.

Exemplary frit binder precursors include feldspar, borax, quartz, sodaash, red lead, zinc oxide, whiting, antimony trioxide, titanium dioxide,sodium silicofluoride, flint, cryolite, boric acid and combinationsthereof. One method of making frits comprises heating a powder of agiven frit material until the powder fuses together, allowing the fusedpowder to cool, and then crushing and screening the fused powder toprovide a very fine powder to be used as a flit binder precursor. In oneembodiment, a frit binder precursor comprises, by weight, 63% silica,12% alumina, 1.2% calcium oxide, 6.3% sodium oxide, 7.5% potassium oxideand 10% boron oxide. The temperature at which a powder is fused togetheris dependant upon the powder chemistry. In one embodiment, thetemperature can be in the range from about 800° C. (1472° F.) to about1800° C. (3272° F.). In another embodiment, the temperature can be inthe range from about 900° C. (1652° F.) to about 1400° C. (2552° F.).Frits may be combined with other ceramic binder precursors to provide aceramic binder precursor to be used in the present invention. In oneembodiment, the ceramic binder precursor may comprise from about 1 to100% frit; in another embodiment, from about 20 to 100% frit. Furtherdetails concerning frit binder precursors may be found in U.S. Pat. No.4,898,597 (Hay), the disclosure of which is incorporated herein byreference.

Useful clay may include crystalline hydrate silicates of aluminum, iron,and magnesium compounds. Examples include, but are not limited to,kaolin, ball clay, fire clay, bentonite, Fuller's earth, activatedclays, calcined clays, colloidal clays.

Useful fluxing minerals may include materials that react at lowtemperatures with other materials present to form a glass phase, thuslowering the required firing temperature of a ceramic binder precursor.In one embodiment, useful fluxing minerals may include alkali oralkaline earth oxides, boric oxide, or lead oxide. Useful examples offluxing minerals include potassium feldspar, sodium feldspar, calciumfeldspar, nepheline syenite, talc, soda ash, borax, and lead oxides.

Silica sols typically comprise silica particles. As used herein, theterm “sol” means a colloidal dispersion of substantially non-aggregated,inorganic oxide particles (e.g., silica particles) in a liquid medium(e.g., aqueous or non-aqueous). Exemplary silica sols in aqueoussolutions include “LUDOX” (obtained from E.I. DuPont de Nemours and Co.,Wilmington, Del. under the trade designation “LUDOX”), “NYACOL”(obtained from Nyacol Co., Ashland, Mass. under the trade designation“NYACOL”), and “NALCO” (obtained from Nalco Chemical Co., Oak Brook,Ill. under the trade designation “NALCO”). Exemplary silica sols innon-aqueous solutions (also called silica organosols) include “NALCO1057” (a silica sol in 2-propoxyethanol) (obtained from Nalco ChemicalCo., Oak Brook, Ill. under the trade designation “NALCO 1057”), “MA-ST,IP-ST” and “EG-ST” (obtained from Nissan Chemical Ind., Tokyo, Japanunder the trade designation “MA-ST, IP-ST” and “EG-ST”). In oneembodiment the colloidal silica particles have an average particlediameter in the range from about 5 to about 100 nanometers. In -anotherembodiment, the particles have an average particle diameter in the rangefrom about 10 to about 50 nanometers. Additional exemplary silica solsare described in U.S. Pat. No. 5,611,829 (Monroe et al.) and U.S. Pat.No. 5,645,619 (Erickson et al.), the disclosures of which areincorporated herein by reference. In another aspect, the pH of a sol maybe adjusted to affect dispersion stability of the sol. In oneembodiment, the pH may be alkaline (e.g., pH in the range from about 8to about 11). In another embodiment, the pH may be acidic (e.g., pH inthe range from about 2 to about 6).

Useful sinterable ceramic powder may include crystalline oxides,non-crystalline oxides, carbides, nitrides, silicides, borides,phosphides, sulfides, tellurides, and selenides. Useful examples ofsinterable ceramic powders include aluminum oxide, silicon oxide,titanium oxide, zirconium oxide, alumina-zirconia, silicon carbide,titanium carbide, titanium boride, aluminum nitride, silicon nitride,ferrites, iron sulfide.

Solid Particulates

Preferably, at least a portion of the plurality of solid particulatesare selected from the group consisting of fillers, grinding aids,fibers, electronically active particulates, pigments, and combinationsthereof. In another embodiment, the plurality of solid particulatesinclude abrasive grains. Typically, the plurality of solid particulatesare selected so they do not decompose during the heating step. In oneembodiment, the plurality of solid particulates have an average particlesize in the range from about 0.5 micrometers to about 1500 micrometers.In another embodiment, the plurality of solid particulates have anaverage particle size in the range from about 10 micrometers to about1500 micrometers. In another embodiment, for example, where the solidparticulate is abrasive grain, the plurality of solid particulates havean average particle size in the range from about 125 micrometers toabout 1500 micrometers. In another embodiment, the plurality ofparticulates have an average particle size in the range from about onemicrometer to about 800 micrometers. In another embodiment for otheruses, the plurality of solid particulates have an average particle sizein the range from about one micrometer to about 400 micrometers. Thesize of the solid particulates means the longest dimension of anindividual solid particulate from a given reference point.

Useful fillers tend to affect properties of the ceramic aggregateprecursor particles, such as, for example, hardness, porosity level,wear behavior, etc. Examples of useful filler materials include metalcarbonates (such as calcium carbonate, chalk, calcite, marl, travertine,marble, limestone, calcium magnesium carbonate, sodium carbonate,magnesium carbonate), pore forming additives (such as wood pulp, woodflour, glass bubbles, glass beads, organic bubbles, organic beads),silica (such as amorphous silica, quartz, glass beads, glass powder,glass bubbles, and glass fibers), silicates (such as talc, clays(montmorillonite), feldspar, mica, calcium silicate, calciummetasilicate, sodium aluminosilicate, sodium silicate), metal sulfates(such as calcium sulfate, barium sulfate, sodium sulfate, aluminumsodium sulfate, aluminum sulfate), aluminum trihydrate, metal oxides(such as calcium oxide (lime), aluminum oxide, titanium dioxide), andmetal sulfites (such as calcium sulfite), greystone, marble, gypsum, Na₂SiF₆, cryolite, vermiculite, and combinations thereof.

“Grinding aid” refers to materials capable of improving the abrasionperformance of an abrasive article upon a metal workpiece whenincorporated into the abrasive coating. In general, the addition of agrinding aid increases the useful life of the abrasive product.Specifically, grinding aids tend to increase the grinding efficiency orcut rate (i.e., the weight of a metal workpiece removed per weight ofabrasive article lost) of an abrasive article upon a metal workpiece.Although not wanting to be bound by theory, it is believed that agrinding aid(s) will (a) decrease the friction between the abrasivematerial and the workpiece being abraded, (b) prevent the abrasiveparticles from “capping” (i.e., prevent metal particles from becomingwelded to the tops of the abrasive particles), or at least reduce thetendency of abrasive particles to cap, (c) decrease the interfacetemperature between the abrasive particles and the workpiece, or (d)decreases the grinding forces. Some examples of useful grinding aidsinclude halide salts, metals, and their alloys. The inorganic halidecompounds will typically break down during abrading and release ahalogen acid or a gaseous halide compound. Examples of halide saltsinclude sodium chloride, potassium cryolite, sodium cryolite, ammoniumcryolite, potassium tetrafluoroborate, sodium tetrafluoroborate, siliconfluorides, potassium chloride, and magnesium chloride. Examples ofmetals include tin, lead, bismuth, cobalt, antimony, cadmium, iron, andtitanium. Other useful grinding aids include sulfur, graphite, andmetallic sulfides. The above-mentioned examples of grinding aids ismeant to be a representative showing of grinding aids, and it is notmeant to encompass all grinding aids.

Useful fibers tend to affect properties of the ceramic aggregateprecursor particles, such as, for example, abrasive properties,electronic properties, reinforcement properties, etc. Exemplary usefulfibers include inorganic oxide, nitride, and carbide compositions.Inorganic fibers may be crystalline or non-crystalline, and may bederived from natural minerals or synthesized from solution, sol, orpolymer precursors. Fibers may be formed by blowing or drawing from amelt, as in the case of conventional glass fibers, or may be fabricatedinto continuous forms by dry or wet spinning processes as in the case ofsome polycrystalline ceramic fibers. Continuous fibers may be furtherprocessed into short, discontinuous lengths and used as solidparticulates.

Useful electronically active particulates include conductiveparticulates (e.g., graphite particulates, carbon black particulates, orother anti-static agents), ferroelectric particulates (e.g.,lead-zirconate-titanate, barium-titanate, andlead-lanthanum-zirconate-titanate), magnetic particulates (e.g.,magnetite, bariumhexaferrite), superconductive particulates, orcombinations thereof.

Exemplary abrasive particulates that are useful in the present inventioninclude fused aluminum oxide abrasive particulates, ceramic aluminumoxide abrasive particulates, white fused aluminum oxide abrasiveparticulates, heat treated aluminum oxide abrasive particulates, brownfused aluminum oxide abrasive particulates, silica abrasiveparticulates, silicon carbide abrasive particulates, green siliconcarbide abrasive particulates, boron carbide abrasive particulates,titanium carbide abrasive particulates, alumina-zirconia abrasiveparticulates, diamond abrasive particulates, ceria abrasiveparticulates, cubic boron nitride abrasive particulates, garnet abrasiveparticulates, or combinations thereof. The ceramic aluminum oxide ispreferably made according to a sol gel process, such as described inU.S. Pat. Nos. 4,314,827; 4,744,802; 4,623,364; 4,770,671; 4,881,951;5,011,508; and 5,213,591, or by a process of sintering anhydrous aluminapowders such as described in U.S. Pat. Nos. 5,593,467; 5,645,618; and5,651,801, the disclosures of which are incorporated herein byreference. The ceramic abrasive grain comprises alpha alumina and,optionally, a metal oxide modifier, such as magnesia, zirconia, zincoxide, nickel oxide, hafnia, yttria, silica, iron oxide, titania,lanthanum oxide, ceria, neodynium oxide, and combinations thereof. Theceramic aluminum oxide may also optionally comprise a nucleating agent,such as alpha alumina, iron oxide, iron oxide precursor, titania,chromia, or combinations thereof. The ceramic aluminum oxide may alsohave a shape, such as that described in U.S. Pat. Nos. 5,201,916 and5,090,968 the disclosures of which are incorporated herein by reference.

Abrasive grains may also have a surface coating. A surface coating canimprove the adhesion between the abrasive grain and the ceramic binderin the abrasive ceramic aggregate particle and/or can alter the abradingcharacteristics of the abrasive grain. Such surface coatings aredescribed in U.S. Pat. Nos. 5,011,508; 1,910,444; 3,041,156; 5,009,675;4,997,461; 5,213,591; and 5,042,991 the disclosures of which areincorporated herein by reference.

An abrasive grain may also contain a coupling agent on its surface, suchas a silane coupling agent. Coupling agents tend to enhance the adhesionbetween a solid surface, such as, for example, abrasive grains andcurable binder precursor. Examples of coupling agents suitable for thisinvention include organo-silanes, zircoaluminates, and titanates. Asused in the present invention, abrasive grains typically have an averageparticle size ranging from about 125 to 1500 micrometers.

Useful abrasive grains typically have a Mohs hardness of at least about7, preferably of at least about 8 and more preferably above 9. Theexpression “Mohs hardness” means a value corresponding to a number onthe “Mohs scale.” “Mohs scale” is defined as a scale of hardness forminerals (see Lafferty, Peter, The Dictionary of Science, p. 386 (1993)or Handbook of Chemistry and Physics, p. F-22 (1975)).

Useful pigment particulates are typically inorganic materials that tendto affect ceramic aggregate particle properties, such as, for example,color, whiteness, or opacity. Exemplary useful pigments include ironoxides, cobalt oxide, manganese dioxide, titanium oxides. Otherexemplary useful pigments include compounds of rare-earth, nickel,cadmium, chromium, and copper elements.

Initiator

In another aspect of the present invention, the composition may furthercomprise initiator selected from the group consisting of photoinitiator,thermal initiator, and combinations thereof. As used in the presentinvention, a thermal initiator may be used when thermal energy is usedin the partial curing step, and photoinitiators may be used whenultraviolet and/or visible light is used in the at least partiallycuring step. The requirement of an initiator may depend on the type ofthe curable binder precursor used and/or the type of energy used in theat least partially curing step (e.g., electron beam or ultravioletlight). For example, phenolic-based curable binder precursors typicallydo not require the addition of an initiator when thermally cured.However, acrylate-based curable binder precursors typically do requirethe addition of an initiator when partially thermally cured. As anotherexample, initiators typically are not required when electron beam energyis used during the partial curing step. However, if ultraviolet orvisible light is utilized, a photoinitiator is typically included in thecomposition.

Upon being exposed to thermal energy, a thermal initiator generates afree radical source. The free radical source then initiates thepolymerization of the curable binder precursor. Exemplary thermalinitiators include organic peroxides (e.g. benzoil peroxide), azocompounds, quinones, nitroso compounds, acyl halides, hydrazones,mercapto compounds, pyrylium compounds, imidazoles, chlorotriazines,benzoin, benzoin alkyl ethers, diketones, phenones, and mixturesthereof. Azo compounds suitable as thermal initiators in the presentinvention may be obtained under the trade designations VAZO 52, VAZO 64and VAZO 67 from E.I. Dupont deNemours and Co., Wilmington, Del.

Upon being exposed to ultraviolet or visible light, the photoinitiatorgenerates a free radical source or a cationic source. This free radicalor cationic source then initiates the polymerization of the curablebinder precursor.

Exemplary photoinitiators that generate a free radical source whenexposed to ultraviolet light include, but are not limited to, thoseselected from the group consisting of organic peroxides (e.g., benzoilperoxide), azo compounds, quinones, benzophenones, nitroso compounds,acyl halides, hydrozones, mercapto compounds, pyrylium compounds,triacrylimidazoles, bisimidazoles, chloroalkytriazines, benzoin ethers,benzil ketals, thioxanthones, and acetophenone derivatives, and mixturesthereof. Examples of photoinitiators that generate a free radical sourcewhen exposed to visible radiation are further described in U.S. Pat. No.4,735,632, the disclosure of which is incorporated herein by reference.

Cationic photoinitiators generate an acid source to initiate thepolymerization of an epoxy resin or a urethane. Exemplary cationicphotoinitiators include a salt having an onium cation and ahalogen-containing complex anion of a metal or metalloid. Other usefulcationic photoinitiators include a salt having an organometallic complexcation and a halogen-containing complex anion of a metal or metalloid.These photoinitiators are further described in U.S. Pat. No. 4,751,138,the disclosure of which is incorporated herein by reference. Anotherexample is an organometallic salt and an onium salt described in U.S.Pat. No. 4,985,340; the disclosure of which is incorporated herein byreference. Still other cationic photoinitiators include an ionic salt ofan organometallic complex in which the metal is selected from theelements of Periodic Groups IVB, VB, VIB, VIIB, and VIIIB. Thesephotoinitiators are further described in U.S. Pat. No. 5,089,536, thedisclosure of which is incorporated herein by reference.

Ultraviolet-activated photoinitiators suitable for the present inventionmay be obtained under the trade designations “IRGACURE 651”, “IRGACURE184”, “IRGACURE 369” and “IRGACURE 819” from Ciba Geigy Company,Winterville, Miss., “Lucirin TPO-L”, from BASF Corp., Livingston, N.J.,and “DAROCUR 1173” from Merck & Co., Rahway, N.J.

In one embodiment, the total amount of initiator (either photoinitiator,thermal initiator, or combinations thereof) may be in the range from 0.1to 10 percent by weight of the curable binder precursor; in anotherembodiment, from about 1 to about 5 percent by weight of the curablebinder precursor. If both photoinitiator and thermal initiator are used,the ratio of photoinitiator to thermal initiator is between about 3.5:1to about 0.5:1.

In another aspect, if ultraviolet or visible light energy is used in theat least partially curing step, the composition may also include aphotosensitizer. Photosensitizer expands the wavelength at which theinitiator or monomer forms free radicals. Exemplary photosensitizersinclude compounds having carbonyl groups or tertiary amino groups andmixtures thereof. Useful examples of compounds having carbonyl groupsare benzophenone, acetophenone, benzil, benzaldehyde,o-chlorobenzaldehyde, xanthone, thioxanthone, 9,10-anthraquinone, andother aromatic ketones. Useful examples of tertiary amines aremethyldiethanolamine, ethyldiethanolamine, triethanolamine,phenylmethylethanolamine, and dimethylaminoethylbenzoate. In oneembodiment, the amount of photosensitizer in the composition may be inthe range from about 0.01 to 10% by weight of the curable binderprecursor. In another embodiment, the amount of photosensitizer in thecomposition may be in the range from about 0.25 to 4% by weight of thecurable binder precursor.

Modifying Additives

Modifying additives are typically included in the composition to modifythe processing characteristics of the composition (e.g., changeviscosity, etc.). Useful examples of modifying additives includecoupling agents, wetting agents, flowing agents, surfactants andcombinations thereof. Many additives tend to decompose during theheating step.

Coupling agents tend to enhance the adhesion between a solid surface(e.g., abrasive grains) and curable binder precursor. Useful examples ofcoupling agents suitable for this invention include organo-silanes,zircoaluminates, and titanates. An abrasive grain may also contain acoupling agent on its surface, such as a silane coupling agent.

Wetting agents, or surfactants, tend to control rheology of thecomposition during processing. In general, any type of wetting agent,i.e., anionic, cationic, nonionic, amphoteric, zwitterionic, etc., canbe employed in the composition. Useful examples of wetting agentsinclude INTERWET 33 from Chemie America Interstab Chemicals, NewBrunswick, N.J.; FLUORAD from 3M Co. St. Paul, Minn. or AEROSOL OT fromRohm Haas, Philadelphia, Pa.

Flowing agents tend to prevent “caking” of powders during processing.For example, a flowing agent may be used in the present invention toprevent ceramic binder precursor from caking during the forming step.Useful examples of flowing agents include condensates of ethylene oxideand unsaturated fatty acids.

Ceramic Aggregate Particles

In one embodiment of the present invention, a composition is formed intoceramic aggregate precursor particles by passing the composition throughan orifice. In one embodiment the particles have an aspect ratio greaterthan one and are rod-shaped. As used herein, the expression “aspectratio” is the longest dimension of the particle (L) divided by theshortest dimension of the particle (W). For example, FIG. 1 illustratesa ceramic aggregate particle made according to a method of the presentinvention with an aspect ratio greater than one. The ceramic aggregateparticle 80 itself comprises a plurality of solid particulates 84 coatedby and embedded in a ceramic binder 82. Optionally, there may existspace 86 void of ceramic binder 82 that is accessible to the outersurface of the particle and suitable to permit fluid penetration. Suchfluid penetration allows the aggregate particle to possess “surfaceconnected porosity”. In one embodiment of the present invention, ceramicaggregate particles have an aspect ratio in the range from about one toabout 30. And in another embodiment, the particles have an aspect ratioin the range from about one to about 10. And in another embodiment, theparticles have an aspect ratio in the range from about one to about 3.

In another aspect, ceramic aggregate particles made according to thepresent invention may have different sizes (e.g., ceramic aggregateparticles with different diameters). For example, in one embodiment, acomposition that is passed through a perforated substrate with circularorifice(s) tends to form ceramic aggregate precursor particles withapproximately circular cross-sections of about the same diameter as theorifice(s). In one embodiment of the present invention, ceramicaggregate particles may have a diameter in the range from about 25micrometers (one mil) to about 12,700 micrometers (500 mils). In anotherembodiment, ceramic aggregate particles may have a diameter in the rangefrom about 381 micrometers (15 mils) to about 6350 micrometers (250mils) in diameter.

One of the features of the present invention is that the aggregateparticles formed as described above have substantially uniformcross-sectional dimension as measured along a designated axis. By“substantially uniform” it is meant that the dimension does not vary bymore than about 20 percent, typically no more than about 10 percent. Inanother aspect, ceramic aggregate particles made according to thepresent invention may have different shapes. For example, the particlesmay have cross-sectional shapes that are approximately circular orpolygonal (e.g., square, triangular, etc.). In another embodiment, theparticles may be crushed to have random shapes.

Method of Making

In another aspect, the present invention involves a method of makingceramic aggregate particles. One embodiment comprises forming acomposition comprising curable binder precursor material, ceramic binderprecursor material, and a plurality of solid particulates into ceramicaggregate precursor particles by passing the composition through atleast one orifice in a perforated substrate, separating the ceramicaggregate precursor particles from the perforated substrate, and atleast partially curing the ceramic aggregate precursor particles.

In forming a composition comprising curable binder precursor material,ceramic binder precursor material, and a plurality of solidparticulates, a variety of weight percentages for each component may beuseful. Exemplary methods according to the present invention may userelatively higher weight percentages of solid particulates (e.g.,abrasive grains) and ceramic binder precursor as compared to curablebinder precursor. Reducing the amount of curable binder precursor may beadvantageous because the curable binder precursor is “burned out” duringthe heating step which may be considered wasteful. In one usefulembodiment, the curable binder precursor material may be in the rangefrom about 5% to about 22% by weight; in another useful embodiment, inthe range from about 7% to about 13% by weight; and in another usefulembodiment, in the range from about 8% to about 10% by weight. In oneuseful embodiment, the ceramic binder precursor material may be in therange from about 11% to about 63% by weight; in another usefulembodiment, in the range from about 22% to about 37% by weight; and inanother useful embodiment, in the range from about 26% to about 31% byweight. In one useful embodiment, the plurality of solid particulatesmay be in the range from about 29% to about 81% by weight; in anotheruseful embodiment, in the range from about 52% to about 70% by weight;and in another useful embodiment in the range from about 60% to about66% by weight. Useful compositions may be organic based, aqueous based,or essentially free of solvent. In one embodiment, the composition maybe less than 10% solvent. In another embodiment, the composition may beless than 0.5% solvent. And in another embodiment, the composition maybe less than 0.1% solvent.

Typically, the passing of the composition through at least one orificein a perforated substrate is achieved by at least one of extruding,milling, or calendering. Preferably, the passing of the compositionthrough at least one orifice is achieved by milling.

FIG. 3 illustrates an apparatus 10 suitable for carrying out a preferredmethod of the present invention. In use, a composition 12 comprisingradiation curable binder precursor material, ceramic binder precursormaterial, and a plurality of solid particulates is fed by gravity from ahopper 14 or by hand into an input 16 of a forming device 18 and passedthrough orifices 21 in a perforated substrate 22 via an applied forcefrom impeller 13 to form rod-shaped ceramic aggregate precursorparticles 20. Particles 20 separate from perforated substrate 22,typically by inherent separation (e.g., due to gravity), mechanicalseparation, or combinations thereof. In general, inherent separation isa function of, for example, the following: 1) the physical and/orchemical properties of the composition (e.g., such as compositionviscosity, size of particulate, magnetic properties if As magneticparticulates are used, electrical properties if electrically chargedparticulates are used), 2) the physical and chemical properties of theprocess equipment that interfaces with the composition (e.g., such asthe impeller properties, perforated substrate properties, magneticfields if magnetic particulates are used, electric fields if electricalparticulates are used), and 3) process operating conditions (e.g., suchas impeller rotation speed, style of impeller, perforated substrateorifice diameter). In particular, as shown in FIG. 3, inherentseparation typically is the result of the formed composition reaching acritical length such that the weight of the particle is greater than anyadhesive force between the formed composition and the perforatedsubstrate, thus the particle falls into container 30. Mechanicalseparation is the result of process equipment mechanically separatingthe formed composition from the perforated substrate. An example ofmechanical separation may be, for example, a doctor blade or air knifelocated on the side of the perforated substrate where the ceramicaggregate precursor particles protrude and moving perpendicular todirection of composition flow, thereby separating the ceramic aggregateprecursor particles from the perforated substrate.

An exemplary perforated substrate may be material with one or moreorifices that has sufficient strength to allow a composition to bepassed through the orifice(s) without rupturing the perforatedsubstrate. In general, perforated substrates may include, for example,mesh screens as described, for example, in U.S. Pat. No. 5,090,968 thedisclosure of which is incorporated herein by reference, film dies,spinneret dies, sieve webs as described, for example, in U.S. Pat. No.4,393,021 or screens as described, for example, in U.S. Pat. No.4,773,599 the disclosures of which are incorporated herein by reference.In one embodiment of the present invention, perforated substratesinclude conical screens with circular orifice(s) in the range from about25 micrometers (one mil) to about 12,700 micrometers (500 mils) indiameter. In another embodiment, perforated substrates include conicalscreens with circular orifice(s) in the range from about 381 micrometers(15 mils) to about 6350 micrometers (250 mils) in diameter.

The forming device 18 in FIG. 3 may be any material forming apparatussuch as, for example, an extruder, milling/size reducing machine,pellitizer or pan agglomerater. FIG. 4 illustrates a preferred formingdevice 40 which is a size-reducing machine, available from Y-Tron Quadro(U.K.) Limited, Chesham, United Kingdom, under the trade designation“QUADRO COMIL.” Forming device 40 has impeller 43 mounted on a rotatableshaft 44. Shaft 44 and impeller 43 are located in channel 46 havinginput 48 and output 50. Impeller 43 is shaped and mounted so that gap 52exists between an outer edge 45 of said impeller 43 and a taperedaperatured wall 58 of screen 56 and gap 52 is substantially constant asthe impeller 43 rotates about shaft 44.

Generally, the cross sectional shape of impeller 43 may be, for example,round, flat or angular flats. Typically, impeller 43 shapes used in thepresent invention are round. In one embodiment, impeller 43 shapes arearrow-head shaped.

Gap 52 width may range, for example, from 25 micometers (1 mil) to 5080micometers (200 mils). Typically, gap 52 width ranges from 127micrometers (5 mils) to 1270 micrometers (50 mils).

Adjusting impeller 43 rotation speed to optimize forming ceramicaggregate precursor particles will be readily apparent to one skilled inthe art. Typically, impeller 43 rotation speed is from 50 to 3500 rpm.

Channel 46 also contains a support 54 shaped and positioned to holdscreen 56 so that any material passing from input 48 to output 50 passesthrough screen 56. Screen 56 30 is formed to have the tapered aperturedwall 58 formed into a frusto-conical shape, with a wide end 60 of thescreen 56 being open and a narrow end 62 being at least partiallyclosed. In most uses, it is desirable to have the narrow end 62completely closed. The screen 56 has orifice(s) 64 that are shaped.

As shown in FIG. 5, screen orifice(s) 64 may be shaped to be curved,circular or polygonal, including, for example, triangles, squares andhexagons. Typically, the shape of screen orifice(s) 64 used in thepresent invention are circular or square. Preferred shapes for screenorifice(s) 64 are square or circular, ranging in size from 381micrometers (15 mil) to 6350 micrometers (250 mil) in diameter oracross.

As can readily be seen from FIG. 4, end 66 of shaft 44 protrudes fromchannel 46. A power source (not shown) can easily be attached to end 66of shaft 44 to cause shaft 44 and attached impeller 43 to rotaterelative to screen 56. Typically, the power source is a variable speedelectric motor. However, the power source is conventional and many otherpower sources will be suitable to operate the apparatus 40.

In another aspect, the present invention involves at least partiallycuring the composition present in the ceramic aggregate precursorparticles. In one embodiment, for example as illustrated in FIG. 3, theceramic aggregate precursor particles become at least partially cured asthey fall by gravity through a curing zone 24. As shown in FIG. 3, atleast partially curing may provide handleable and collectable ceramicaggregate precursor particles 28, which may be collected in container30.

The at least partially curing of the ceramic aggregate precursorparticles may be caused by an energy source 26. Exemplary energysource(s) 26 include thermal and radiation energy. Typically, aradiation energy source(s) is used. Exemplary sources of radiationenergy are electron beam, ultraviolet light, visible light, microwave,laser light and combinations thereof.

In one embodiment, ultraviolet light is used as a radiation energysource 26 and mirrors 25 are used in a curing zone 24 to reflect theultraviolet waves in a way that intensifies the energy transmitted tothe ceramic aggregate precursor particles. Ultraviolet radiation refersto non-particulate radiation having a wavelength within the range ofabout 4 to about 400 nanometers, preferably in the range of about 250 toabout 400 nanometers. In one embodiment, an apparatus used for at leastpartially radiation curing is one such as that available from Fusion UVSystems, Inc., Gaithersburg, Md., under the trade designation “DRE 410Q”. In one embodiment, the “DRE 410 Q” radiation apparatus is equippedwith, for example, two 600 watt “d” fusion lamps that are set on “high”power.

Visible radiation refers to non-particulate radiation having awavelength within the range of about 400 to about 800 nanometers. In oneembodiment, non-particulate radiation having a wavelength in the rangeof about 400 to about 550 nanometers is used.

In other embodiments, a thermal energy source(s) may be used. Exemplarysources of thermal energy that may be utilized include electrical orcombustion heat sources. In another embodiment, infrared radiation maybe used as a source of thermal energy.

The amount of radiation energy needed to at least partially cure theceramic aggregate precursor particles to provide handleable andcollectable ceramic aggregate precursor particles may depend uponfactors such as, for example, the type of curable binder precursormaterial, the type of ceramic binder precursor material, residence timein the curing zone, the type of solid particulates and the type of, ifany, optional modifying additives.

Optionally, ceramic aggregate precursor particles made according to amethod of the present invention may be further at least partially curedusing thermal energy, radiation energy, or combinations thereof. Furtherat least partially curing may provide ceramic aggregate precursorparticles with different properties such as, for example, increasedrigidity for handling and collecting. Typically, ceramic aggregateparticles that are handleable and collectable tend to remain cohesiveceramic aggregate precursor particles through the method steps.Typically, ceramic aggregate particles that are not handleable andcollectable tend to break apart if the particles are physically moved ata point during the method steps. In one embodiment, first ceramicaggregate precursor particles are at least partially cured to providesecond ceramic aggregate precursor particles comprising curable binderprecursor material, ceramic binder precursor material, a plurality ofsolid particulates, and the product of at least partially curing thefirst ceramic aggregate precursor particles. The method furthercomilprises at least partially curing the second ceramic aggregateprecursor particles that are handleable and collectable.

In one embodiment of the present invention, after at least partiallycuring the ceramic aggregate precursor particles, the next step involvesheating the ceramic aggregate precursor particles to a temperature andfor a time sufficient to provide ceramic aggregate particles withdesired properties, such as, for example, Total Pore Volume (ml/g),Apparent Particle Volume (ml/g), Volume Percent Porosity, Apparent BulkDensity (g/cm³), or Crush Strength (lb). Total Pore Volume and ApparentParticle Volume are measured by mercury intrusion porosimetry analysis.Mercury intrusion porosimetry analysis is described further in Examples9-14. Total Poie Volume is the mass-normalized total volume of openspace within the ceramic aggregate particle that is connected to theouter surface of the particle, i.e., surface connected porosity, whichallows penetration of mercury, due to capillary action, into the ceramicaggregate particle. Mercury intrusion porosimetry measures penetrationof mercury into particles with pore diameters smaller than about 900micrometers. Typically, the aggregate particles of the invention haveVolume Percent Porosities of up to 25 percent. Volume Percent Porosityis calculated as follows: (Total Pore Volume/Apparent ParticleVolume)×100. Apparent Particle Volume is the volume of mercury displacedby the ceramic aggregate particle. Apparent Bulk Density is the ratio ofthe ceramic aggregate particle mass to Apparent Particle Volume. CrushStrength is the average force required to cause a particle to breakunder a compressive load and is described further in Test Procedure #2.Exemplary values produced by methods of the present invention arediscussed below.

In one embodiment, heating includes the following two-step firingprocess. The two steps of the firing process are usually performed atseparate times, but could be completed sequentially at the same time inone firing furnace cycle. In one embodiment, the first (i.e.,pre-firing) step involves heating the ceramic aggregate precursorparticles from room temperature to a final temperature in the range fromabout 500° C. to about 650° C. at a slow rate, typically 2° C. perminute and exposing the particles to the final temperature for about 1to about 4 hours typically, in order to remove cured and/or uncuredmaterial, such as, for example, acrylate resin, and to cause the ceramicbinder precursor material to sufficiently bond together to providehandleable and collectable particles. Typically, as heating during thefirst step progresses, ceramic aggregate precursor particle CrushStrength decreases to a minimum. This minimum typically occurs uponcomplete pyrolysis of cured and/or uncured material because thepyrolysis of any cured and/or uncured material leaves spatial voids inthe ceramic aggregate precursor particles and the ceramic binderprecursor material typically has not sufficiently bonded together toprovide handleable and collectable particles. However, as heatingcontinues towards the final temperature, the ceramic binder precursormaterial typically starts to sufficiently bond together to cause theparticle Crush Strength to increase and to provide handleable andcollectable particles. Because the particles are typically nothandleable and collectable upon complete pyrolysis, a static bed istypically used during the first step to minimize applied forces to theparticles so that the particles remain intact. Examples of firing kilnssuitable for static bed firing in the first step include shuttle kilns,roller hearth kilns, pusher plate kilns, and belt furnace kilns. In oneembodiment a slow rate of heating, for example 2° C. per minute, theceramic aggregate precursor particles during the first step is performedto control the rate of pyrolysis of cured and/or uncured material.Typically, relatively fast heating rates tend to cause cured and/oruncured material to decompose into gas(es) at a rate which most likelydestroys the ceramic aggregate precursor particles. Typically, heatingin the pre-firing step is in an oxidizing atmosphere (e.g., air) to aidin complete pyrolysis of any cured and/or uncured material, such as, forexample, acrylate resin. It is preferred that pre-firing temperaturesand heating rates are selected to ensure that all cured and/or uncuredmaterial is removed from the precursor ceramic aggregate particles atcompletion of the pre-firing step.

Typically, in the second firing step, pre-fired particles containing noresidual cured and/or uncured material are heated to a final temperaturein the range from about 650° C. to about 1500° C. at any desired heatingrate. Again, it is preferred that no residual cured and/or uncuredmaterial is present in the pre-fired particles since evolution of gasesfrom thermal decomposition of the materials may cause particle fracture,thus interfering with desired particle shape uniformity. Typically, theparticles are exposed to the final temperature for one to four hours inorder to cause partial or complete densification of the ceramic binderprecursor material. As used in the present invention, “densification”means the partial or complete elimination of open space within theceramic aggregate particle to provide ceramic aggregate particles withincreased particle density (i.e., decreased particle volume per unitparticle mass). In one embodiment, heating during the second firing stepmay occur in a static bed or non-static bed because pre-fired particlesare handleable and collectable and remain intact if subjected to anapplied force that tends to strain or deform a body. Examples ofnon-static beds include rotary kiln or fluidized bed firing techniques.

The final firing temperature and the exposure time of the particles tothe final firing temperature affect Total Pore Volume (ml/g), Volume %Porosity, Apparent Bulk Density (g/cm³), and Crush Strength (lb). BothTotal Pore Volume and Volume % Porosity of ceramic aggregate particlestends to decrease as the final firing temperature increases and/or asthe exposure time of the ceramic aggregate particles to the final firingtemperature increases. In one embodiment, Total Pore Volume may be inthe range from about 0.01 mu/g to about 0.05 ml/g. In anotherembodiment, Total Pore Volume may be in the range from about 0.002 m1/gto about 0.25 ml/g. In one embodiment, Volume % Porosity may be in therange from about 25% to about 5%. In another embodiment, Volume %Porosity may be in the range from about 40% to about 1%. Apparent BulkDensity tends to increase as the final firing temperature increasesand/or as the exposure time of the ceramic aggregate particles to thefinal firing temperature increases. In one embodiment, Apparent BulkDensity may be in the range from about 2.5 g/cm³ to about 3.0 g/cm³. Inanother embodiment, Apparent Bulk Density may be in the range from about2.0 g/cm³ to about 4.0 g/cm³. Crush Strength tends to increase as thefinal firing temperature increases and/or as the exposure time of theceramic aggregate particles to the final firing temperature increases.In one embodiment, Crush Strength may be in the range from about 5 lb.(2.3 kg) to about 25 lb. (11.3 kg). In another embodiment, CrushStrength may be in the range from about 2 lb. (0.9 kg) to about 80 lb.(36.3 kg).

Typically, at least partially cured ceramic aggregate precursorparticles are at least partially coated with a metal oxide particulateto prevent them from sticking to one another during heating. If firingsteps are performed at separate times, the ceramic aggregate precursorparticles are typically coated with metal oxide particulate afterpre-firing but before the second firing step. In one embodiment, thequantity of metal oxide particulate used to at least partially coat theceramic aggregate precursor particles is approximately 5%-10% by weightof the ceramic aggregate precursor particles. In one embodiment, metaloxide particulate includes hydrous alumina.

In another embodiment, methods according to the present invention mayinvolve reducing the average size of ceramic aggregate precursor and/orceramic aggregate particles after at least partially curing and/orheating respectively. Typically, reducing the average particle size isperformed using at least one of milling, crushing, or tumbling. In oneembodiment, apparatus 40 shown in FIG. 4 may be used to reduce theaverage size of ceramic aggregate precursor particles and/or ceramicaggregate particles.

Ceramic aggregate particles made according to methods of the presentinvention can be used in, for example, abrasives, roofing granules,filtration products, hard coatings, shot blast media, tumbling media,brake linings, anti-slip and wear resistant coatings, synthetic bone,dental compositions, retro-reflective sheeting and laminate compositestructures. In one embodiment, methods according to the presentinvention involve combining at least a portion of the cured ceramicaggregate particles with abrasive article binder material and abrasivematerial to provide an abrasive article. Suitable abrasive articlesinclude coated abrasive articles (including nonwoven abrasive articles)and bonded abrasive articles.

Abrasive ceramic aggregates according to the present invention can beused in conventional abrasive products, such as coated abrasiveproducts, bonded abrasive products (including vitrified, resinoid, andmetal bonded grinding wheels, cutoff wheels, mounted points, and honingstones), nonwoven abrasive products, and abrasive brushes. Typically,abrasive products (i.e., abrasive articles) include binder and abrasiveparticles (which in practicing the present invention includes abrasiveaggregates according to the present invention), secured within theabrasive product by the binder. Methods of making such abrasive productsand using abrasive products are well known to those skilled in the art.Furthermore, abrasive aggregates according to the present invention canbe used in abrasive applications that utilize slurries of abradingcompounds (e.g., polishing compounds), milling media, shot blast media,vibratory mill media and the like.

Coated abrasive products generally include a backing, abrasive material,and at least one binder to hold abrasive particles (which in practicingthe present invention includes abrasive particles aggregated together inthe form of abrasive ceramic aggregate according to the presentinvention) onto the backing. The backing can be any suitable material,including cloth, polymeric film, fiber, nonwoven webs, paper,combinations thereof, and treated versions thereof. The binder can beany suitable binder, including an inorganic or organic binder (includingthermally curable resins and radiation curable resins). The abrasiveparticles can be present in one layer or in two layers of the coatedabrasive product.

An example of a coated abrasive product is depicted in FIG. 6. Referringto this figure, coated abrasive product 101 has a backing (substrate)102 and abrasive layer 103. Abrasive layer 103 includes abrasive ceramicaggregate according to the present invention 104 secured to a majorsurface of backing 102 by make coat 105 and size coat 106. In someinstances, a supersize coat (not shown) is used.

Bonded abrasive products typically include a shaped mass of abrasiveparticles (which in practicing the present invention includes abrasiveceramic aggregate), held together by an organic, metallic, or vitrifiedbinder. Such shaped mass can be, for example, in the form of a wheel,such as a grinding wheel or cutoff wheel. The diameter of grindingwheels typically is about 1 cm to over 1 meter; the diameter of cut offwheels about 1 cm to over 80 cm (more typically 3 cm to about 50 cm).The cut off wheel thickness is typically about 0.5 mm to about 5 cm,more typically about 0.5 mm to about 2 cm. The shaped mass can also bein the form, for example, of a honing stone, segment, mounted point,disc (e.g. double disc grinder) or other conventional bonded abrasiveshape. Bonded abrasive products typically comprise about 3-50% by volumebond material, about 30-90% by volume abrasive material, up to 50% byvolume additives (including grinding aids), and up to 70% by volumepores, based on the total volume of the bonded abrasive product.Typically, grinding wheels have at least 10%, 20%, or even moreporosity.

An exemplary bonded abrasive is a grinding wheel. Referring to FIG. 7,grinding wheel 110 is depicted, which includes abrasive ceramicaggregate according to the present invention 111, molded in a wheel andmounted on hub 112. An advantage that embodiments of abrasive aggregateaccording to the present invention may offer in a bonded abrasive suchas a grinding wheel is room for chip clearance during metal removal.That is, the porosity present in certain embodiments of abrasiveaggregates according to the present invention may provide room for chipclearance during metal removal.

Nonwoven abrasive products typically include an open porous loftypolymer filament structure having abrasive particles (which inpracticing the present invention includes abrasive ceramic aggregatesaccording to the present invention), distributed throughout thestructure and adherently bonded therein by an organic binder. Examplesof filaments include polyester fibers, polyamide fibers, and polyaramidfibers. In FIG. 8, a schematic depiction, enlarged about 100×, of atypical nonwoven abrasive product is provided. Such a nonwoven abrasiveproduct comprises fibrous mat 150 as a substrate, onto which abrasiveceramic aggregates according to the present invention 152 are adhered bybinder 154.

Useful abrasive brushes include those having a plurality of bristlesunitary with a backing (see, e.g., U.S. Pat. Nos. 5,427,595 (Pihl etal.), 5,443,906 (Pihl et al.), 5,679,067 (Johnson et al.), and 5,903,951(lonta et al.), the disclosure of which is incorporated herein byreference). Such brushes include those made by injection molding amixture of polymer and abrasive particles (which in practicing thepresent invention includes abrasive ceramic aggregates according to thepresent invention).

Suitable organic binders for making abrasive products includethermosetting organic polymers. Examples of suitable thermosettingorganic polymers include phenolic resins, urea-formaldehyde resins,melamine-formaldehyde resins, urethane resins, acrylate resins,polyester resins, aminoplast resins having pendant α,β-unsaturatedcarbonyl groups, epoxy resins, acrylated urethane, acrylated epoxies,and combinations thereof. The binder and/or abrasive product may alsoinclude additives such as fibers, lubricants, wetting agents,thixotropic materials, surfactants, pigments, dyes, antistatic agents(e.g., carbon black, vanadium oxide, graphite, etc.), coupling agents(e.g., silanes, titanates, zircoaluminates, etc.), plasticizers,suspending agents, and the like. The amounts of these optional additivesare selected to provide the desired properties. The coupling agents canimprove adhesion to the abrasive particles and/or filler. The binderchemistry may be thermally cured, radiation cured or combinationsthereof. Additional details on binder chemistry may be found in U.S.Pat. Nos. 4,588,419 (Caul et al.), 4,751,137 (Tumey et al.), and5,436,063 (Follett et al.), the disclosures of which are incorporatedherein by reference.

More specifically with regard to vitrified bonded abrasives, vitreousbonding materials, which exhibit an amorphous structure and aretypically hard, are well known in the art. Bonded, vitrified abrasiveproducts may be in the shape of a wheel (including cut off wheels),honing stone, mounted pointed or other conventional bonded abrasiveshape. An exemplary vitrified bonded abrasive product is a grindingwheel.

Examples of metal oxides that are used to form vitreous bondingmaterials include: silica, silicates, alumina, soda, calcia, potassia,titania, iron oxide, zinc oxide, lithium oxide, magnesia, boria,aluminum silicate, borosilicate glass, lithium aluminum silicate,combinations thereof, and the like. Typically, vitreous bondingmaterials can be formed from composition comprising from 10 to 100%glass frit, although more typically the composition comprises 20% to 80%glass frit, or 30% to 70% glass frit. The remaining portion of thevitreous bonding material can be a non-frit material. Alternatively, thevitreous bond may be derived from a non-frit containing composition.Vitreous bonding materials are typically matured at a temperature(s) inthe range from about 700° C. to about 1500° C., usually in the rangefrom about 800° C. to about 1300° C., sometimes in the range from about900° C. to about 1200° C., or even in the range from about 950° C. toabout 1100° C. The actual temperature at which the bond is matureddepends, for example, on the particular bond chemistry.

Exemplary vitrified bonding materials include those comprising silica,alumina (e.g., at least 10 percent by weight alumina), and boria (e.g.,at least 10 percent by weight boria). In most cases the vitrifiedbonding material further comprise alkali metal oxide(s) (e.g., Na₂O andK₂O) (in some cases at least 10 percent by weight alkali metaloxide(s)).

Binder materials may also contain filler materials or grinding aids,typically in the form of a particulate material. Typically, theparticulate materials are inorganic materials. Examples of usefulfillers and grinding aids for this invention have been described earlierherein.

The abrasive products can contain 100% abrasive ceramic aggregateaccording to the present invention, or blends of such aggregates withother abrasive particles and/or diluent particles. However, at leastabout 2% by weight, more commonly at least about 5% by weight, and evenmore commonly about 30-100% by weight, of the abrasive particles in theabrasive products should be abrasive ceramic aggregates according to thepresent invention. In some instances, the abrasive aggregate accordingthe present invention may be blended with other abrasive particlesand/or diluent particles at a ratio between 5 to 75% by weight, about 25to 75% by weight, about 40 to 60% by weight, or about 50% to 50% byweight (i.e., in equal amounts by weight). Examples of suitable abrasiveparticles include, but are not limited to, fused aluminum oxide(including white fused alumina, heat treated aluminum oxide and brownaluminum oxide), silicon carbide, silicon nitride, boron carbide,titanium carbide, diamond, cubic boron nitride, garnet, fusedalumina-zirconia, sol-gel-derived abrasive particles, and the like. Thesol-gel-derived abrasive particles may be seeded or non-seeded.Likewise, the sol-gel-derived abrasive particles may be randomly shapedor have a shape associated with them, such as a triangle. Examples ofsol gel abrasive particles include those described above. The abrasiveaggregate may have essentially the same size as the diluent particle.Conversely, the abrasive aggregate may be larger in size than thediluent particle. Further, additional useful fused abrasive particlesare disclosed, for example, in applications having U.S. Ser. Nos.09/618,876; 09/618,879; 09/619,106; 09/619,191; 09/619,192; 09/619,215;09/619,289; 09/619,563; 09/619,729; 09/619,744, and 09/620,262, eachfiled on Jul. 19, 2000, and 09/772,730, filed Jan. 30, 2001, thedisclosure of which is incorporated herein by reference.

Abrasive ceramic aggregates according to the present invention can alsobe combined with other abrasive agglomerates. The binder of the otherabrasive agglomerates may be organic and/or inorganic. Additionaldetails regarding abrasive agglomerates may be found, for example, inU.S. Pat. Nos. 4,311,489 (Kressner), 4,652,275 (Bloecher et al.),4,799,939 (Bloecher et al.), 5,549,962 (Holmes et al.), and 5,975,988(Christianson), the disclosures of which are incorporated herein byreference.

Examples of suitable diluent particles include marble, gypsum, flint,silica, iron oxide, aluminum silicate, glass (including glass bubblesand glass beads), alumina bubbles, alumina beads and diluentagglomerates.

The abrasive particles may be uniformly distributed in the abrasivearticle or concentrated in selected areas or portions of the abrasivearticle. For example in a coated abrasive, there may be two layers ofabrasive particles/grain. The first layer comprises abrasiveparticles/grain other than those according to the present invention, andthe second (outermost) layer comprises abrasive ceramic aggregateaccording to the present invention. Likewise in a bonded abrasive, theremay be two distinct sections of the grinding wheel. The outermostsection may comprise abrasive ceramic aggregates according to thepresent invention, whereas the innermost section does not.Alternatively, abrasive ceramic aggregates according to the presentinvention may be uniformly distributed throughout the bonded abrasivearticle.

Further details regarding coated abrasive products can be found, forexample, in U.S. Pat. Nos. 4,734,104 (Broberg), 4,737,163 (Larkey),5,203,884 (Buchanan et al.), 5,152,917 (Pieper et al.), 5,378,251(Culler et al.), 5,417,726 (Stout et al.), 5,436,063 (Follett et al.),5,496,386 (Broberg et al.), 5, 609,706 (Benedict et al.), 5,520,711(Helmin), 5,954,844 (Law et al.), 5,961,674 (Gagliardi et al.), and5,975,988 (Christinason), the disclosures of which are incorporatedherein by reference. Further details regarding bonded abrasive productscan be found, for example, in U.S. Pat. Nos. 4,543,107 (Rue), 4,741,743(Narayanan et al.), 4,800,685 (Haynes et al.), 4,898,597 (Hay et al.),4,997,461 (Markhoff-Matheny et al.), 5,038,453 (Narayanan et al.),5,110,332 (Narayanan et al.), and 5,863,308 (Qi et al.) the disclosuresof which are incorporated herein by reference. Further, detailsregarding vitreous bonded abrasives can be found, for example, in U.S.Pat. Nos. 4,543,107 (Rue), 4,898,597 (Hay), 4,997,461 (Markhoff-Mathenyet al.), 5,094,672 (Giles et al.), 5,118,326 (Sheldon et al.),5,131,926(Sheldon et al.), 5,203,886 (Sheldon et al.), 5,282,875 (Woodet al.), 5,738,696 (Wu et al.), and 5,863,308 (Qi), the disclosures ofwhich are incorporated herein by reference. Further details regardingnonwoven abrasive products can be found, for example, in U.S. Pat. No.2,958,593 (Hoover et al.), the disclosure of which is incorporatedherein by reference.

Methods for abrading with abrasive aggregates according to the presentinvention may range from snagging (i.e., high pressure high stockremoval) to polishing (e.g., polishing medical implants with coatedabrasive belts), wherein the latter is typically done with finer grades(e.g., less ANSI 220 and finer) of abrasive particles. The abrasiveaggregates may also be used in precision abrading applications, such asgrinding cam shafts with vitrified bonded wheels. The size of theabrasive aggregates grain (and abrasive particles comprising suchaggregates) used for a particular abrading application will be apparentto those skilled in the art.

Abrading with abrasive articles according to the present invention maybe done dry or wet. For wet abrading, the liquid may be introducedsupplied in the form of a light mist to complete flood. Examples ofcommonly used liquids include: water, water-soluble oil, organiclubricant, and emulsions. The liquid may serve to reduce the heatassociated with abrading and/or act as a lubricant. The liquid maycontain minor amounts of additives such as bactericide, antifoamingagents, and the like.

Abrasive aggregates according to the present invention may be used toabrade workpieces such as aluminum metal, carbon steels, mild steels,tool steels, stainless steel, hardened steel, titanium, glass, ceramics,wood, wood like materials, paint, painted surfaces, organic coatedsurfaces and the like. The applied force during abrading typicallyranges from about 1 to about 100 kilograms.

Abrasive aggregates according to the present invention may be also beused in loose form or in a slurry wherein abrasive aggregate isdispersed in liquid medium (e.g., water).

Referring again to FIG. 1, in one embodiment the solid particulates 84are abrasive grains and the binder 82 is present in a relatively lowvolume ratio of, for example, 0.2 to 2.0. This provides an aggregatecomprising principally abrasive grain (preferable 125-1500 micron size).Binder 82 conforms closely to the outermost surfaces 88 of the solidparticles. Normally the thickness of the binder 82 on the outermostsurfaces 88 of the particles is relatively thin and is dependent uponthe size of the particles. Typically, the thickness of the binder 82 isabout 10 percent or less of the cross-sectional dimension of theparticle, usually between about 0.05 microns and 1500 microns. Suchaggregates can, in certain embodiments, provide abrasive articles withconsistently high cut rates for longer periods of time. For example,abrasive articles having cut rates of up to 200 percent, and life timesof up to 500 percent (typically 200-500 percent) based upon comparativeproducts, have been obtained. The abrasive article using such aggregatesprovides more consistent performance including work piece finish overtime. Additionally, the increased surface are of the aggregateparticulates caused by the high degree of conformity of binder 82 toabrasive grains 84, provides a particulate which adheres strongly to themake coat of abrasive articles incorporating or carrying theseparticulates.

The following examples will further illustrate specific embodiments ofthe present invention. Those of ordinary skill in the art will recognizethat the present invention also includes modifications and alterationsof the embodiments set out in the examples and that the illustrativeexamples do not limit the scope of the claimed invention.

EXAMPLES

The following abbreviations are used in the examples (All parts,percentages, ratios, etc., in the examples are by weight unlessotherwise indicated):

AO: heat treated fused aluminum oxide abrasive grain, commerciallyavailable from Treibacher, Villach, Austria under the trade designation“ALODUR BFRPL”.

AOP: alpha-aluminum oxide powder, commercially available from Alcoaunder the trade designation “A-16 SG”.

ASF: amorphous silica filler, commercially available from DeGussa Corp.(Richfield Part, N.J.), under the trade designation “OX-50”.

AG321: sol gel-derived alumina-based abrasive grain commerciallyavailable from 3M Company, St. Paul, Minn. under the trade designation“Cubitron 321”.

BP: boehmite (gamma-alumina monohydrate), commercially available fromCondea Chemical, Hamberg, Germany under the trade designation“Disperal”.

CaCO3: calcium carbonate filler, commercially available from J. M. HuberCorp., Quincy, Ill., under the trade designation “Chem Q 325”.

CH: cumene hydroperoxide, commercially available from Aldrich ChemicalCo., Milwaukee, Wis. as item no. 24,750-2.

CRY: sodium cryolite, commercially available from Tarconard Trading a/s,Avemakke Nyberg, Denmark, under the trade designation “RTN”.

IO: red iron oxide powder, commercially available from ElementisPigments Inc., E. St. Louis, Ill., under the trade designation “KromaRO-8097”.

KB1: photo initiator 2,2-dimethoxy- 1,2-diphenyl-1-ethanone,commercially available from Sartomer Co. under the trade designation“ESACURE KB1”.

KBF4: potassium tetrafluoroborate SPEC 102 and 104 commerciallyavailable from Atotech USZ Inc., Cleveland, Ohio

PET: 5 mil (125 micron) thick polyester film with ethylene acrylic acid(EAA) co-polymer primer, commercially available from 3M Company, St.Paul, Minn., under the trade designation “Scotchpar P990”.

PH2: photo initiator2-benzyl-2-N,N-dimethylamino-1-(4-morpholinophenyl)-1-butanone,commercially available from Ciba Geigy Corp. under the trade designation“Irgacure 369”.

REO: solution prepared by blending a lanthanum, neodymium, and yttriumnitrate solution [20.5% La(NO₃)₃.6H₂O, 20.1% Nd(NO₃)₃.6H₂O, 26.1%Y(NO₃)₃.6H₂O; available from Molycorp of Lourviers, CO] with asufficient amount of MGN and cobalt nitrate [15% Co(NO₃)₃.6H₂O;available from Hall Chemical of Wickliffe, Ohio] to provide a solutioncontaining about 5.8% La(NO₃)₃.6H₂O, about 5.8% Nd(NO₃)₃.6H₂O, about7.1% Y(NO₃)₃.6H₂O, about 14.4% Mg(NO₃)₃.6H₂O, about 0.4% Co(NO₃)₃.6H₂O,and the balan deionized water.

SC: silicon carbide abrasive grain, commercially available from 3MCompany, St. Paul, Minn.

SCA: silane coupling agent 3-methacryloxpropyl-trimethoxysilane,commercially available from OSI Specialties, Inc., Greenwich, Conn.,under the trade designation “A-174”.

SGP: alumino-boro-silicate glass powder, 325 mesh, commerciallyavailable from Specialty Glass Inc., Oldsmar, Fla., under the tradedesignation “SP1086”.

TATHEIC: triacrylate of tris(hydroxyethyl)isocyanurate, commerciallyavailable from Sartomer Co. under the trade designation “SR368”.

TMPTA: trimethylol propane triacrylate, commercially available fromSartomer Co. under the trade designation “SR351”.

Procedure #1

General Procedure for Making a Ceramic Aggregate Precursor Slurry

An abrasive slurry was prepared by thoroughly mixing abrasive grain,glass powders, acrylate resin, and initiators, using a mixer (obtainedfrom Hobart Corporation, Troy, Ohio; model number A120T). Specificformulations can be found in Tables 2, 4, 6, 9, 12, and 13. The abrasiveslurry was mixed in the mixer on low speed using a flat-beater styleimpeller for 30 minutes and heated to a temperature within the rangefrom about 90° F. (32° C.) to about 120° F. (49° C.) due to mechanicalheating and heat of reaction. At this point, the abrasive slurry wasvery thick with cement-like handling characteristics. The mixed slurrywas then placed in a refrigerator for at least 45 minutes to cool beforefurther processing. The temperature of the refrigerator was in the rangefrom about 40° F. (4° C.) to about 45° F. (7° C.).

Procedure #2

General Procedure for Making Ceramic Aggregate Precursor Particles

The ceramic aggregate precursor slurry was formed into aggregateprecursor particles with the aid of the “QUADRO COMIL” material formingapparatus (obtained from Quadro Incorporated, Milbourne, N.J. under thetrade designation “QUADRO COMIL”; model number 197). Depending on thedesired cross sectional shape of the ceramic aggregate precursorparticles, different shaped orifices were used. Conical screens withcircular shaped hole orifices were used to produce ceramic aggregateprecursor particles with circular shaped cross sections. Conical screenswith square shaped hole orifices could also be used to produce ceramicaggregate precursor particles with square shaped cross sections. Theslurry was added to the hopper of the “QUADRO COMIL” by hand while theimpeller was spinning at a preset speed (rpm) of 350 rpms. The rotatingimpeller forced the slurry through the orifices in the conical screenand when a critical length (typically, a critical length is reached whenthe weight of the particle is greater than any adhesive force betweenthe formed composition and the perforated substrate) was reached, thefilamentary shaped ceramic aggregate precursor particles separated fromthe outside of the screen, and fell by gravity through a UV curingchamber (obtained from Fusion UV Systems, Gaithersburg, Md.; model #DRE410 Q) equipped with two 600 watt “d” Fusion lamps set at “high” power.The ceramic aggregate precursor particles were at least partially curedby exposure to the UV radiation and thereby converted into handleableand collectable particles.

In some of the examples below the ceramic aggregate precursor particleswere further at least partially cured by placing the particles inaluminum pans and at least partially thermally curing them in aforced-air oven (obtained from Lindberg/Blue M Company, Watertown, Wis.;model number POM-246F) for about 5 hours to about 8 hours and at about340° F. (171° C.) to about 360° F. (182° C.). Optionally, the at leastpartially cured ceramic aggregate precursor particles were reduced insize by passing them through the “QUADRO COMIL”. Typically, particlesare reduced in size by passing them through the “QUADRO COMIL,” with the“QUADRO COMIL” equipped with conical screens that have relatively largerorifices than those used for forming ceramic aggregate precursorparticles (see examples for specific details). For particle sizereduction, the impeller rotation speed of the “QUADRO COMIL” was set at252 rpm.

Procedure #3

General Procedure for Heating Ceramic Aggregate Precursor Particles tomake Ceramic Aggregate Particles

In the examples below, rod-shaped ceramic aggregate precursor particleswere converted into rod-shaped ceramic aggregate particles by a two-stepfiring process. The two steps of the firing process were carried out atseparate times, but could optionally be completed sequentially in onefiring furnace cycle.

First Firing Step (i.e., pre-firing)

In the first firing step, rod-shaped ceramic aggregate precursorparticles were pre-fired in order to remove acrylate resin used in theparticle forming process described in Procedure #2, and to cause theceramic binder precursor material to sufficiently bond together toprovide handleable and collectable particles. Ceramic aggregateprecursor particles were reduced in size to provide an average particlesize (see examples for specific average particle sizes) to provideceramic aggregate particles suitable to make coated abrasive articles.Then the particles were spread ⅝ inch (16 mm) thick in 3.5 inch ×7.5inch (89 mm×190 mm) aluminum pans (obtained from Coors Ceramics Co.,Golden Colo.) and heated in air in a laboratory furnace (obtained fromLindberg/Blue M Company, Watertown, Wis.; model number BF 117) accordingto the following schedule:

a. about 3.6° F. (2° C.)/minute heating rate from about room temperatureto about 662° F. (350° C.)

b. about a 2 hour soak at about 662° F. (350° C.)

c. about 3.6° F. (2° C.)/minute from about 662° F. (350° C.) to about1157° F. (625° C.)

d. about a 1 hour soak at about 1157° F. (625° C.)

e. furnace cool to about room temperature (the furnace was shut off, theparticles remained in the furnace, and both the furnace and theparticles cooled at an uncontrolled rate to about room temperature).

After the pre-fire step, the ceramic aggregate particles were crushed byhand pressure to break up longer filamentary particles and particleclusters that had bonded together. In Examples 2-6, the ceramicaggregate particles were used after the pre-fired state without furtherheat treatment for grinding tests.

Second Firing Step for Examples #1 and #7-#14

In the second firing step for Examples #1 and #7-#14, pre-fired ceramicaggregate particles were re-heated from room temperature to a finaltemperature in the range from about 1200° F. (650° C.) to about 1832OF(1000° C.) in order to cause partial or complete densification of theceramic binder precursor material. In preparation for the final firing,pre-fired particles were placed in a 500 ml glass jar along with 10% wtBP. The mixture was then tumbled by hand for approximately one minute tocoat the particles to prevent them from sticking to one another in thesubsequent high-temperature firing step. BP-coated particles were placedin the alumina trays and fired in the laboratory furnace (obtained fromLindberg/Blue M Company, Watertown, Wis.; model number BF 117) accordingto the following schedule:

a. about 9° F. (5° C.)/minute heating rate from about room temperatureto final temperature in the range from about 1200° F. (650° C.) to about1832° F. (1000° C.)

b. about a 4 hour soak at final temperature in the range from about1200° F. (650° C.) to about 1832° F. (1000° C.)

c. furnace cool to about room temperature (the furnace was shut off, theparticles remained in the furnace, and both the furnace and theparticles cooled at an uncontrolled rate to about room temperature)

Fired ceramic aggregate particles were then tumbled in apolyethylene-lined cement mixer (obtained from CF Glico Inc., Grafton,Wis., model number 59016A) for 15 minutes to break up clusters ofparticles. The fired particles were then screened using a ro-tap sieveshaker, model number RX 29, and 8 inch (20.3 cm) diameter brass sieves(obtained from W.S. Tyler, Mentor, Ohio; model number RX 29) to removethe alumina dust and to collect the desired ceramic aggregate particlesizes (see examples for specific particle size). Screened particles wererinsed with deionized water to remove residual alumina dust and thewashed particles were then spread in an alumina pan and dried overnightin a forced-air oven at 212° F. (100° C.) (obtained from DespachIndustries, Minneapolis, Minn.; model number ALD2-11).

Second Firing Step for Examples #15-#19

In the second firing step for Examples #15-#19, pre-fired ceramicaggregate particles were re-heated to a final temperature of about 2732°F. (1500° C.) in order to cause partial or complete densification of theceramic binder precursor. Approximately 100 grams of pre-fired ceramicaggregate particles were placed in 3 inch diameter platinum cruciblesand then heated in a laboratory box furnace (obtained from CM,Bloomfield, N.J., under the trade designation “CM RAPID TEMP”) accordingto the following schedule:

a. about 9° F. (5° C.)/minute heating rate from about room temperatureto final temperature of about 1500° C.

b. about a 90 minute soak at final temperature of about 1500° C.

c. furnace cool to about room temperature (the furnace was shut off, theparticles remained in the furnace, and both the furnace and theparticles cooled at an uncontrolled rate to about room temperature)

The fired particles were then screened using a ro-tap sieve shaker,model number RX 29, and 8 inch (20.3 cm) diameter brass sieves (obtainedfrom W. S. Tyler, Mentor, OH; model number RX 29) to remove the aluminadust and to collect the desired ceramic aggregate particles size (seeexamples for specific sizes). Screened particles were rinsed withdeionized water to remove residual alumina dust and the washed particleswere then spread in an aluminum pan and dried overnight for about 10hours in a forced-air oven at about 212° F. (100° C.) (obtained fromDespach Industries, Minneapolis, Minn.; model number ALD2-11).

Procedure #4

General Procedure for Making film-backed Coated Abrasive Articles usingCeramic Aggregate Particles made According to the Present Invention

Examples of coated abrasive articles with film backings and acrylatemake and size resins were prepared using ceramic aggregate particlesafter the first firing step and/or second firing step. Make and sizecoat resin was prepared according to the formulation listed in Table 1.Quantities are listed as weight percentages.

TABLE 1 Make and size coat resin formulation for film-backed abrasivearticles Material Quantity (%) TMPTA 39.4 TATHEIC 16.9 PH2 0.6 SCA 2.0KBF4 39.2 ASF 2.0

PET film 0.005 inch (127 um) thick was used for the backing. The filmhad a 0.0008 inch (20 micrometers) thick EAA prime coating. The makeresin was knife-coated 0.012 inch (300 micrometers) thick onto theprimed surface of the film using a six inch universal draw-down knife(obtained from Paul Gardner, Pompano Beach, Calif., model numberAP-G06). Ceramic aggregate particles were poured by hand onto the wetresin and rolled back and forth by hand several times to distribute theparticles evenly on the backing, and then the excess particles wereshaken off. The resulting coated sample was then taped onto a metalplate and cured by placing the sample on a conveyor and passing itthrough a UV cure system (obtained from Fusion UV Systems, Gaithersburg,Md.; model #DRE 410 Q) using a 600 watt “d” Fusion UV lamp set at “high”power. The coated sample was passed three times through the UV curesystem at about 30 ft/min (9.1 meters/min). The coated sample was thenflexed over a 2 inch (5 cm) diameter bar in order to make the coatedsample more suitable for installation into the Rocker Drum Testapparatus (see Test Procedure #1 below). A thin size coating of the sameresin mixture used for the make coat was then applied by hand onto thecoated sample with a paint brush and the excess resin was blotted offwith a paper towel. The size coated sample was then passed through theUV cure system three times at about 30 ft/min (9.1 meters/min). Thecured coated sample was then flexed again over a 2 inch (5 cm) diameterbar in order to make the coated sample more suitable for installationinto the Rocker Drum Test apparatus (see Test Procedure #1 below).

Procedure #5

General Procedure for Making Cloth-backed Coated Abrasive Articles usingCeramic Aggregate Particles made According to the Present Invention

Examples of coated abrasive articles with polyester cloth backings andphenolic-based make and size resins were prepared with ceramic aggregateparticles made according to the present invention. The Y-weight backingcloth was a sateen weave polyester with a basis weight of approximately535 g/m² (obtained from Wisselink Textiles, Aalten, Netherlands). Themake resin was a 52:48 mixture by weight of CaCO₃:water-based phenolic(obtained from Georgia-Pacific Resins, Columbus, Ohio; product numberGP23155B). An “ACCU LAB” draw-down apparatus (obtained from Paul GardnerCo., Pompano Beach, Fla., under the trade designation “ACCU LAB”) and a#90 wire-wound coating rod (obtained from Paul Gardner Co., PompanoBeach, Fla.) was used to spread a uniform coating of make resin onto thepolyester backing. The make coating weight for the #90 wire woundcoating rod setting on the “ACCU LAB” was approximately 230 g/m² on adry weight basis. Make coating weight was determined for a given settingof the #90 wire wound coating rod on the “ACCU LAB” by the followingprocedure: weighing a backing sample, applying a make coat to thebacking sample using the “ACCU LAB” apparatus at a given setting, dryingthe make coat in a convection oven (obtained from Precision Scientific,Chicago, Ill.; model number 8) about 2 hours at about 190° F. (88° C.),and then weighing the dried make coated backing. Coating weight=(driedmake coated backing sample weight—the backing sample weight)/(area ofthe backing sample). Ceramic aggregate particles made according to thepresent invention were then poured by hand onto the wet make resin androlled back and forth by hand several times to distribute the particlesevenly on the backing, and then the excess particles were shaken off.Coated samples were heated overnight for about 10 hours in a convectionoven (obtained from Precision Scientific, Chicago, Ill.; model number 8)set at about 180° F. (82° C.). The size resin was a 52:48 mixture byweight of cryolite:water-based phenolic (obtained from Georgia-PacificResins, Columbus, Ohio; product number GP23155B) and was applied to thesamples by hand with a paint brush. The size coated samples were heatedin a convection oven (obtained from Precision Scientific, Chicago, Ill.;model number 8) for about 1 hour at about 180° F. (82° C.), and thencured for about 2 hours at about 200° F. (93° C.), followed by about 30minutes at about 220° F. (104° C.) and about 1 hour at about 245° F.(118° C.). After curing, the coated abrasive samples were flexed over a2 inch (5 cm) diameter bar in order to make the coated sample moresuitable for installation into the Rocker Drum Test apparatus (see TestProcedure #1 below).

Test Procedure #1

Rocker Drum

Abrasive articles made according to Procedure 4 or 5 were cut into 10inch×2.5 inch (25.4 cm×6.4 cm) sheets. These samples were installed on acylindrical steel drum of a testing machine. The steel drum was 13inches (33 cm) in diameter, and was driven by an electric motor and apushrod lever so that the drum oscillated (rocked back and forth in asmall arc). A 1018 carbon steel workpiece (a workpiece is abraded by theabrasive article), {fraction (3/16)} inch (0.48 cm) square, was fixed ina lever arm arrangement above the abrasive sample, and a load of about 8lb (3.6 kg) was applied to the workpiece. As the abrasive article rockedback and forth, the workpiece was abraded, and a {fraction (3/16)}inch×5.5 inch (0.48 cm×14 cm) wear path was created on the abrasivearticle. There were approximately 60 strokes per minute on this wearpath. A compressed air stream at 20 psi (138 kPa) was directed onto thesample to clear grinding swarf and debris from the wear path. The amountof steel removed after each 1000 cycles (one cycle being oneback-and-forth motion) was recorded as the “interval cut” and the “totalcut” was the cumulative (total of “interval cuts”) amount of steelremoved at the endpoint of the test. The endpoint of the test wasdetermined to be when a predetermined number of cycles were completed orwhen the cut rate dropped to less than approximately 40% of the maximuminterval cut recorded for that test. This procedure is referred toherein as a “rocker drum test”.

Test Procedure #2

Crush Test

Approximately 5 grams of ceramic aggregate particles were used for eachtest. Particles were crushed by hand and particles that were in therange from about 1 mm to about 2 mm were tested. The crushed ceramicaggregate particles were poured onto an epoxy resin lab bench top andspread out by hand to isolate individual particles. Then the particleswere tested using a force gauge equipped with a flat compression footfitting (obtained from Shimpo Instruments, Lincolnwood, Ill.; modelnumber FGV-50). The force gauge read from 0 to 60 lbs. The flatcompression foot of the force gauge was held in a horizontal positionabove and contacting the particle to be crushed and a constant force wasapplied by hand until the particle broke (particle breakage was measuredby audible sound and/or feel). The maximum force applied to cause theparticle to break (i.e., Crush Test Value) was recorded and the testrepeated. The reported Crush Test Value was an average of at least 40particles from a given sample.

Comparative Example A

Film-backed coated samples were prepared using organically-bondedagglomerate abrasive particles (obtained from 3M Co, St. Paul, Minn.under the trade designation “MULTICUT C”). “MULTICUT C” particlesinclude P100 AG321 grade abrasive grains bonded together by acryolite-filled phenolic bond system. The coated samples were madeaccording to Procedure #4, but #100 “MULTICUT C” particles weresubstituted for ceramic aggregate particles made. according to thepresent invention.

Comparative Example B

The coated abrasive articles made in Comparative Example B were preparedusing a single layer of P100 AG321 grade abrasive grainselectrostatically coated on a polyester backing using CaCO3-filledphenolic make resin and cryolite-filled phenolic size resin. TheY-weight backing cloth was a sateen weave polyester with a basis weightof approximately 331 g/m² (obtained from Milliken & Co., Lagrange, Ga.).The make resin was a 52:48 by weight mixture including CaCO₃-filledwater-based phenolic resin (obtained from Georgia-Pacific Resins,Columbus, Ohio; product number GP23155B). The wet resin coating weightwas approximately 150 g/m². 330 gm² of AG321, grade P100 abrasive grainswere applied electrostatically to provide a coated abrasive article. Themake coat was then precured in a forced-air oven (obtained from DespachIndustries, Minneapolis, Minn.; model number type S) for about 30minutes at about 175° F. (79° C.) and about 90 minutes at about 200° F.(93° C.). Then a cryolite-filled water-based phenolic size coat wasapplied with a wet coating weight of approximately 177 g/m². The sizecoat was precured in the oven for about 30 minutes at about 175° F. (79°C.) and about 120 minutes at about 200° F. (93° C.). The coated materialwas then final cured in the oven for about 10 hours at about 212° F.(100° C.) and then flexed over a 2 inch (5 cm) bar in order to make thecoated sample more suitable for installation into the Rocker Drum Testapparatus (see Test Procedure #1 below).

Example #1

Example #1 demonstrates that ceramic aggregate particles can be preparedaccording to the method of the present invention using grade #100abrasive grit and non-crystalline binder precursor. Ceramic aggregateprecursor slurry was prepared as described in Procedure #1, using amixer (obtained from Hobart Corporation, Troy, Ohio; model number A120T)and AG321 grade P100 abrasive grain. The abrasive slurry formulation islisted in Table 2 and was combined by combining the ingredients in Table2 in the order listed in the table. The final temperature of theabrasive slurry after mixing was approximately 90° F. (32° C.).

TABLE 2 Example 1 abrasive slurry formualtion Material Quantity (g)TMPTA 346.5 KB1 3.5 SGP 672 P100 AG321 2018 Total inorganic solidscontent 88 wt %

Ceramic aggregate precursor particles were made as described inProcedure #2. The “QUADRO COMIL” was set up with a small round impellarand a 0.075 inch (19 mm) gap and a conical screen with 0.045 inch (11mm) round orifices. The drive motor speed was set at 1600 rpm. Pre-firedparticles were reduced in size with one additional pass through the“QUADRO COMIL”. Precursor particles were prefired as described inProcedure #3. Prefired particles were then reduced in size with oneadditional pass through the “QUADRO COMIL” before final firing accordingto Procedure #3, except that the final firing temperature was at about1697° F. (925° C.). The fired ceramic aggregate particles were screened,and the size fraction that passed through a #16 mesh screen and retainedon a #20 mesh screen was collected. The screened particles were used tomake film-backed coated abrasive articles according to Procedure #4.Coated samples of Example #1 were tested according to the Rocker-Drumtest procedure (test procedure #1) and compared with samples madeaccording to Comparative Examples A and B. The results are summarized inTable 3.

TABLE 3 Rocker-Drum test for Example #1 and Comparative Examples A and BComparative Comparative Test interval Example A Example B Example #1(cycles) Interval Cut (g) Interval Cut (g) Interval Cut (g) 1000 1.031.43 1.23 2000 1.09 1.20 1.26 3000 1.05 0.48 1.31 4000 1.05 0.23 1.305000 1.03 — 1.28 6000 0.97 — 1.26 7000 0.96 — 1.31 8000 0.84 — 1.29 90000.50 — 1.38 10000  0.13 — 1.05 11000  — — 0.89 12000  — — 0.70 Total Cut(g) 8.65 3.34 14.26 

The results in Table 3 show that the abrasive article made in Example #1provided interval cut rates (grams/1000 cycles) between 30 to 50% higherthan the abrasive article made in Comparative Example A throughout thetest. In the first 1000 cycles, Example #1 achieved a cut rate of 86% ofthe abrasive article made in Comparative Example B, and exceeded the cutrate of Comparative Example B for the balance of the test. The total cutof example #1 was 165% of Comparative Example A and 427% of ComparativeExample B.

Comparative Example C

The abrasive articles made in Comparative Example C were cloth-backedand were coated with organically-bonded agglomerate abrasive particles(obtained from 3M Co, St. Paul, Minn. under the trade designation“MULTICUT C”). Grade #60 “MULTICUT C” particles include grade #60 AG321abrasive grains bonded together by a cryolite-filled phenolic bondsystem. The coated samples were made according to Procedure #4, but #60“MULTICUT C” particles were substituted for ceramic aggregate particlesmade according to the present invention.

Comparative Example D

The abrasive articles made in Comparative Example D were commerciallyavailable coated abrasive articles (obtained from 3M Co., St. PaulMinn., under the trade designation “3M 967F”). “3M 967F” grade #60included a single layer of AG321 grade #60 abrasive grainselectrostatically coated onto a polyester cloth backing with phenolicbased make and size resins.

Examples #2-#5

Ceramic aggregate particles produced for Examples #2-#5 demonstrated theuse of larger grit size abrasive (grade #60) and non-crystalline ceramicbinder precursor. In particles for Example #2, the weight ratio ofabrasive grit to non-crystalline binder precursor was 1.5, and inExample #3, the weight ratio of abrasive grit to non-crystalline binderprecursor was 3.0. In Examples #4 and #5, two different ceramicaggregate particle sizes were combined in fabricating coated abrasivearticles. Ceramic aggregate precursor slurries were prepared asdescribed in Procedure #1, using AG321 grade #60 abrasive grain. Theabrasive slurry formulation is listed in Table 4 and was combined byfirst combining the ingredients in Table 4 in the order listed exceptfor the SGP and AG321 grade #60. The SGP and AG321 grade #60 were firstcombined together and then slowly added to the remaining ingredients inTable 4.

TABLE 4 Abrasive slurry formulations for Examples #2-#5 Example #2 and#4 Example #3 and #5 Material Quantity (g) Quantity (g) TMPTA 891 594KB1 9.0 6.0 CH 4.0 4.0 SGP 2120 1509 #60 AG 321 4527 Total inorganicsolids content 86 wt % 91 wt %

Mixing was done in a mixer with a flat beater rotor and on the slowestspeed setting (obtained from Hobart Corporation, Troy, Ohio; modelnumber A120T). After the SGP/AG321 mixture was added to the resinmixture, the speed was increased to “medium”. Mixing was continued forabout 25 minutes as described in Procedure #1. The final temperature ofthe mixture was in the range from about 100° F. (38° C.) to about 120°F. (49° C.).

Ceramic aggregate precursor particles were made as described inProcedure #2. Particles made for Examples #2 and #4 were kept separatefrom particles made for 5 Examples #3 and #5 through all making andfiring processes. The “QUADRO COMIL” was set up with a small roundimpellar, a 0.075 inch (1.90 mm) gap, a conical screen with 0.062 inch(1.57 mm) round grater-type orifices, and the drive motor speed was setat 470 rpm. After passing the slurries through the “QUADRO COMIL” and UVcuring system, the at least partially cured precursor particles wereplaced in aluminum pans and thermally-cured in a forced-air oven(obtained from Lindberg/Blue M Company, Watertown, Wis.; model numberPOM-246F) for about 6 hours at about 350° F. (177° C.). After being atleast partially thermally cured the ceramic aggregate precursorparticles were reduced in size with one additional pass through the“QUADRO COMIL” using a 0.075 inch (1.90 mm) gap and a 0.094 inch (2.39mm) grater screen. The particles were then prefired as described inProcedure #3. The prefired, ceramic aggregate particles were screenedusing a vibratory grader (obtained from Exolon Co., Tanawanda, N.Y.,model number 501) and a #24 mesh stainless steel screen (obtained fromCambridge Wire Cloth Co., Cambridge, Md.). Particles that passed throughthe #24 mesh screen (“fine” particle size) were separated from theparticles that were retained on the #24 mesh screen (“coarse” particlesize). Both particle sizes were collected and used to make coatedabrasive articles to be tested.

The screened particles were used to make cloth-backed coated abrasivearticles according to Procedure #5. For Examples #2 and #3, only the“coarse” particles were used to make coated abrasive articles. ForExamples #4 and #5, the coarse particles were coated onto the samplefirst and then the open space between the “coarse” particles waspartially filled by applying the “fine” particles to make coatedabrasive articles according to Procedure #5. All coated samples weredried, sized, and cured as described in Procedure #3. Coated samples ofExamples #2-#5 were tested according to the Rocker-Drum test procedure(test procedure #1) and compared with the samples of ComparativeExamples C and D. For these tests the endpoint of the test was after18,000 cycles or when the cut rate for a sample dropped to less thanabout 40% of the maximum interval cut recorded for that sample. The testresults are summarized in Table 5.

TABLE 5 Rocker-Drum test for Examples #2-#5 and Comparative Examples Cand D Compara- Compara- tive Ex- tive Ex- Exam- Exam- Exam- Exam- Testample C ample D ple #2 ple #3 ple #4 ple #5 interval Interval IntervalInterval Interval Interval Interval cycles cut (g) cut (g) cut (g) cut(g) cut (g) cut (g)  1000 1.14 1.74 0.99 1.21 1.33 1.18  2000 1.30 1.821.24 1.43 1.75 1.33  3000 1.42 1.72 1.42 1.47 1.84 1.38  4000 1.46 1.431.42 1.51 1.86 1.49  5000 1.48 0.53 1.54 1.57 1.85 1.51  6000 1.59 —1.54 1.47 1.75 1.53  7000 1.60 — 1.63 1.26 1.77 1.57  8000 1.74 — 1.500.97 1.87 1.65  9000 1.61 — 1.43 0.78 1.85 1.65 10000 1.53 — 1.48 0.601.75 1.54 11000 1.51 — 1.44 0.55 1.39 1.31 12000 1.25 — 1.30 0.41 0.871.12 13000 0.78 — 1.38 0.36 — 1.03 14000 — — 1.20 — — 0.81 15000 — —0.98 — — 0.69 16000 — — 0.73 — — 0.42 17000 — — 0.54 — — — 18000 — —0.36 — — — Total 18.48  7.24 22.12  13.59  19.88  20.21  Cut (g)

As shown in Table 5, some coated samples made with ceramic aggregateparticles made according to the present invention provided total cuts of108% to 120% of that for Comparative Example C, and 275% to 305% of thatfor Comparative Example D. The total cut of the abrasive article made inExample #3 was limited by premature shelling of the particles from thebacking.

Examples #6-#8

The abrasive articles made in Examples #6-#8 were designed todemonstrate the effect that firing temperature, used to make ceramicaggregate particles, has on cut performance of abrasive articles. Theceramic aggregate particles used to make abrasive articles in examples#6-#8 were also designed to demonstrate that two grades of abrasivegrains can be used in a method of the present invention to produceceramic aggregate particles.

Ceramic aggregate precursor slurry was prepared as describe in Procedure#1, using a combination of AG321 grades #60 and #320 abrasive grains.The abrasive slurry formulation is listed in Table 6 and was combined byfirst combining the ingredients in Table 6 in the order listed exceptfor the SGP and AG321 grades #60 and #320. The SGP and AG321 grades #60and #320 were first combined together and then slowly added to theremaining ingredients in Table 6.

TABLE 6 Abrasive slurry formulation for Examples #6-#8 Material Quantity(g) TMPTA 600 KB1 6.0 CH 4.0 SCA 50.0 SGP 1600 #60 AG321 3200 P320 AG321800 Total inorganic solids content 90 wt %

Mixing was done in a mixer with a flat beater rotor and on the slowestspeed setting (obtained from Hobart Corporation, Troy, Ohio; modelnumber A120T). After the SGP/AG321 mixture was added to the resinmixture, the speed was increased to “medium”. Mixing was continued forabout 25 minutes as described in Procedure #1. The final temperature ofthe mixture was about 100° F. (38° C.). Ceramic aggregate precursorparticles were made as described in Procedure #2. The “QUADRO COMIL” wasset up with a solid impeller (Arrow 1701), a 0.075 inch (1.90 mm) gap, aconical screen with 0.050 inch (1.27 mm) round, grater-type orifices,and the drive motor was set at 253 rpm. After passing the slurry throughthe “QUADRO COMIL” and UV curing system, the at least partially-curedceramic aggregate precursor particles were placed in aluminum pans andthermally-cured in a forced-air oven (obtained from Lindberg/Blue MCompany, Watertown, Wis.; model number POM-246F) for about 6 hours atabout 350° F. (177° C.). The ceramic aggregate precursor particles werethen reduced in size by causing them to pass through the “QUADRO COMIL”using a 0.075 inch (1.90 mm) gap and a 0.062 inch (1.57 mm) graterscreen. After the reduction in size the ceramic aggregate precursorparticles were screened to get rid of fine “dust” using a vibratorygrader (obtained from Exolon Co., Tanawanda, N.Y., model number 501) anda #36 mesh stainless steel screen (obtained from Cambridge Wire ClothCo., Cambridge, Md.). Particles that were retained on the #36 meshscreen were collected.

Particles for Example #6 were prefired and screened according toProcedure #3. Particles that passed through a #16 mesh screen but wereretained on a #30 mesh screen were retained and used to make samples forExample #6. Particles for Examples #7 and #8 were fired as described inProcedure #3. The final temperatures in the second firing step wereabout 1382° F. (750° C.) and about 1697° F. (925° C.) for Example #7 andExample #8 respectively. Then the particles for Examples #7 and #8 werescreened and washed as described in Procedure #3. Particles that passedthrough a #16 mesh screen but were retained on a #30 mesh screen wereretained and used to make samples for Examples #7 and #8.

The particles made for Examples #6-#8 were used to make cloth-backedcoated abrasive articles as described in Procedure #5. A single coatingof fired particles was applied and the coated samples dried, sized andcured according to Procedure #5. The abrasive articles of Examples #6-#8were tested on the Rocker-Drum according to Test Procedure #1 andcompared with the abrasive articles of Comparative Examples C and D. Forthese tests, the endpoint was after 6000 Rocker-Drum cycles werecompleted. The tests results are summarized in Table #7.

TABLE 7 Rocker-Drum test results for Examples #6-#8 ComparativeComparative Example Example Example Test Example C Example D #6 #7 #8interval Interval Interval Interval Interval Interval (cycles) cut (g)cut (g) cut (g) cut (g) cut (g) 1000 1.20 1.80 1.13 1.51 1.77 2000 1.331.79 1.37 1.79 2.10 3000 1.40 1.91 1.46 1.89 2.27 4000 1.46 1.84 1.511.95 2.31 5000 1.47 1.28 1.60 2.11 2.39 6000 1.51 0.21 1.74 2.14 2.28Total 8.37 8.83 8.81 11.39  13.12  cut (g)

As shown in Table 7, the abrasive article made in Example #8 made withceramic aggregate particles fired at about 1697° F. (925° C.), provideda total cut of about 150% of the abrasive article in ComparativeExamples C and D. The abrasive article in Example #8 achieved a maximumcut rate of about 158% of the abrasive article in Comparative Example Cand of about 125% of the abrasive article in Comparative Example D. Theeffect of increased firing temperature on ceramic aggregate particles isreflected by the increasing total cut and maximum cut rates for theabrasive articles in Examples #7 and #8, as compared with that inExample #6.

Examples #9-#14

The particles used in Examples #9-#14 show the effect of increasingfiring temperature in the second firing step in Procedure #3 on theCrush Strength and porosity of ceramic aggregate particles. The ceramicaggregate particles used to make abrasive articles in Example #2 wereused as particles in Examples #9-#11. For Example #9, the particles wereused as made for Example #2. For Examples #10 and #11, the particleswere “re-fired” according to the second firing step described inProcedure #3 to final firing temperatures listed in Table 8. The ceramicaggregate particles used to make abrasive articles in Example 3 wereused as particles in Examples #12-#14. For Example #12, the particleswere used as made for Example #3. For Examples #13 and #14, the prefiredparticles from Example #3 were fired according to the second firing stepin Procedure #3 to final firing temperatures listed in Table 8. Table 8also lists the following physical properties of the ceramic aggregateparticles: Total Pore Volume, Volume Percent Porosity, Apparent BulkDensity, and average Crush Strength. Total Pore Volume and ApparentParticle Volume were measured by mercury intrusion porosimetry analysis,using a “MICROMETIRICS AUTO PORE” instrument (obtained fromMicromeritics Corp., Norcross Ga., under the trade designation“MICROMETIRICS AUTO PORE”). Total Pore Volume is the mass-normalizedtotal volume of open space within the ceramic aggregate particle that isconnected to the outer surface of the particle that allows penetrationof mercury, due to capillary action, into the ceramic aggregateparticle. Mercury intrusion porosimetry allows measures penetration ofmercury into particles with pore diameters in the range from about 0.07micrometers to about 900 micrometers. Volume Percent Porosity iscalculated as follows: (Total Pore Volume/Apparent Particle Volume) 100.Apparent Particle Volume is the volume of mercury displaced by theceramic aggregate particle. Apparent Bulk Density is the ratio of theceramic aggregate particle mass to Apparent Particle Volume. CrushStrength is the average force required to cause a particle to breakunder a compressive load and is described further in Test Procedure #2.

TABLE 8 Physical properties for Examples #9-#14 EXAMPLE 9 10 11 12 13 14Firing 625/1 750/4 925/4 625/1 750/4 925/4 Conditions Temperature (°C.)/ Time (hr) Total Pore 0.061 0.019 0.007 0.055 0.042 0.012 Volume(mL/g) Volume % 15.71 5.37 2.09 15.38 12.22 3.74 Porosity Apparent 2.572.77 2.87 2.79 2.90 3.24 Bulk Density (g/cc) Crush 17.9 52.2 >>60 7.321.2 44.0 Strength (exceeded (lb) test gage capacity)

Examples #15-#19

The ceramic aggregate particles in Examples #15-#19 are designed todemonstrate the use of crystalline ceramic binder precursor material(e.g., alpha alumina powder) and fused aluminum oxide, ceramic aluminumoxide, or silicon carbide abrasive particulates to make ceramicaggregate particles. The ceramic aggregate precursor particles inExamples #15-#19 were prepared in a similar manner as the ceramicaggregate precursor particles in Examples #6-#8. Ceramic aggregateprecursor slurries were prepared as described in Procedure #1, usingeither AG321 abrasive grain (for Examples #15 and #16), AO abrasivegrain (for Examples #17 and #18) or SC abrasive grain (for Example #19).In Examples #15-#19, the ceramic binder precursor material SGP, used inExamples #6-#8, was replaced with AOP. The abrasive slurry formulationsfor Examples #15-#19 are shown in Table 9 and were combined by firstmixing together the ingredients in Table 9 in the order listed exceptfor the AOP and AG321 grades #60 and #320 (Examples #15 and #16), the AOgrade #80 (Examples #17 and #18), or the SC grade #80 (Example #19). Ineach of these examples, the AOP was first combined with the AG321 grade#60 and #320, the AO grade #80, or the SC grade #80, and the combinedmixtures were then slowly added to the remaining ingredients in Table 9.

TABLE 9 Abrasive slurry formulations for Examples #15-#19 Example #15Example #17 and #16 and #18 Example #19 Material Quantity (g) Quantity(g) Quantity (g) TMPTA 300 150 300 KB1 3.0 1.5 3.0 CH 2.0 1.0 2.0 SCA15.0 4.0 8.0 AOP 1000 550 1100 #60 AG321 2000 — — P320 AG321 500 — — P80AO — 1375 — P80 SC — — 2750 Total inorganic 92 wt % 93 wt % 93 wt %solids content

Mixing was done in a mixer with a flat beater rotor and on the slowestspeed setting (obtained from Hobart Corporation, Troy, Ohio; modelnumber A120T). After the AOP/AG321, AOP/AO or AOP/SC mixture was addedto the resin mixture, the speed was increased to “medium”. Mixing wascontinued for about 25 minutes as described in Procedure #1. The finaltemperature of each mixture was about 116° F. (47° C.). Ceramicaggregate precursor particles were made for examples #15-#19 asdescribed in Procedure #2. The “QUADRO COMIL” setup was the same forExamples #15-#19, using a solid impeller (Arrow 1701) with a 0.175 inch(4.44 mm) gap and a conical screen with 0.050 inch (1.27 mm) round,grater-type orifices. The drive motor was operated at 350 rpm. Afterpassing the slurries through the “QUADRO COMIL” and UV curing system,the at least partially cured ceramic aggregate precursor particles wereplaced in aluminum pans and at least partially thermally cured in theforced-air oven for about 6 hours at about 350° F. (177° C.). Theceramic aggregate precursor particles were then reduced in size bycausing them to pass through the “QUADRO COMIL” using a carbide-tippedArrow 1607 impeller at a 0.175 inch (4.44 mm) gap and a 0.079 inch (2.00mm) grater screen. After the reduction in size the ceramic aggregateprecursor particles were screened and the particle size fraction greaterthan #36 mesh (0.0185 inch, 0.47 mm) was collected.

Ceramic aggregate particles made for Examples #15-#19 were made asdescribed in Procedure #3, except that in the prefire step the particleswere held at a maximum temperature of about 1832° F. (1000° C.) forabout 4 hours. Also, the BP coating described in Procedure #3 was notused to make the ceramic aggregate particles in Examples #15-#19. Also,after pre-firing, ceramic aggregate precursor particles for Examples#15-#18 were further reduced in size by again causing them to passthrough the “QUADRO COMIL” using a carbide-tipped Arrow 1607 impeller ata 0.0175 inch (4.44 mm) gap and using a 0.079 inch (2.0 mm) graterscreen. After further reduction in size, the ceramic aggregate precursorparticles were screened as described in Procedure #3, and the particlesize fraction larger than 20 mesh (0.0320 inch, 0.81 mm) and smallerthan 12 mesh (0.0661 inch, 1.70 mm) was collected.

For Examples #15, #17 and #19, the second firing step according toProcedure #3 was performed by placing about 100 grams of screened,prefired ceramic aggregate particles in a 3 inch (7.6 cm) diameterplatinum crucible and then heating in a laboratory box furnace (obtainedfrom CM Rapid Temp Furnace, Bloomfield N.J. under the trade designation“RAPID TEMP”). In the second firing step, the particles were held at amaximum temperature of about 2732° F. (1500° C.) for about 90 minutes.The particles were then allowed to cool to room temperature by shuttingoff the “RAPID TEMP” box furnace and allowing it to cool to roomtemperature.

For Examples #16 and #18 prefired ceramic aggregate particles wereimpregnated with REO sintering aid solution before the second firingstep. The pre-fired ceramic aggregate particles were impregnated bymixing 25 ml of REO solution per 100 grams of prefired particles withthe prefired particles. The mixture was tumbled in a rotating,polyethylene-lined container for about 10 minutes to distribute the REOsolution through the particles. Impregnated particles were then placedin aluminum pans and placed in a forced-air oven (obtained from DespachIndustries, Minneapolis, Minn.; model number ALD2-11) and dried forabout 2 hours at about 100° C. The particles were then removed andallowed to cool down to about room temperature. Then the particles werepassed through a rotary kiln that was heated to about 1200° F. (650°C.). The rotary kiln had a “hot zone” that was about 12 inches (30.5 cm)and a silicon carbide rotary tube that was about 15 cm in diameter,about 1.1 m long, and was elevated at about 2.5° inclination. Theparticle residence time was about 5 minutes through the length of thetube. After being passed through the rotary kiln the particles were thenfired at about 2732° F. (1500° C.) for about 90 minutes according to thesecond firing step for the ceramic aggregate particles used in Examples#15, #17 and #19.

The ceramic aggregate particles made for Examples #15-#18 were used tomake cloth-backed coated abrasive articles as described in Procedure #5.A single coating of ceramic aggregate particles was applied to the clothbacking and the coated samples dried, sized and cured according toProcedure #5. The abrasive articles of Examples #15-#18 were tested andcompared against abrasive articles of Comparative Examples C and D onthe Rocker-Drum according to Test Procedure #1. The test results aresummarized in Table 10. Particle Crush Strength Values were measuredaccording to Test Procedure #2. For these tests, the endpoint was after9000 Rocker-Drum cycles were completed or when the cut rate for a sampledropped to less than about 30% of the maximum interval cut recorded forthat sample. The Rocker-Drum test results are summarized in Table 10.

TABLE 10 Rocker drum test results for Examples #15-#18 Com- Com-parative parative Exam- Exam- Exam- Exam- Exam- Exam- ple ple ple pleTest ple C ple D #15 #16 #17 #18 interval Interval Interval IntervalInterval Interval Interval cycles cut (g) cut (g) cut (g) cut (g) cut(g) cut (g) 1000 1.13 1.81 2.14 1.03 2.14 1.08 2000 1.29 1.79 2.32 1.162.42 1.18 3000 1.32 1.78 2.33 1.16 2.38 1.24 4000 1.39 1.77 2.33 1.182.43 1.25 5000 1.36 1.61 2.28 1.14 2.39 1.22 6000 1.41 1.17 2.02 1.162.41 1.17 7000 1.48 0.24 1.54 1.11 2.45 1.12 8000 1.47 — 1.44 1.08 2.561.08 9000 1.51 — 1.19 1.02 2.52 0.95 Total 12.36  10.17  17.59  10.04 21.70  11.21  Cut (g)

Table 10 shows that the ceramic aggregate particles made in Example #17,which included alumina and REO, provided a maximum cut rate of 170% ofthat for the abrasive article in Comparative Example C and of 140% ofthat for the abrasive article in Comparative Example D. Compared to theabrasive article made in Example #17, the corresponding abrasive articlemade in Example #15, which used ceramic aggregate particles that did notinclude REO, provided similar cut rates initially, but the total cutprovided by the abrasive article in Example #15 was limited by shellingof the particles from the backing after about 5000 test cycles. Theabrasive article made in Example #17 maintained a consistent cut rate,as measured by the interval cuts, within a range of about 18% fromlowest to highest over the duration of the test. The cut rate, asmeasured by the interval cuts, of the abrasive article in ComparativeExample C increased steadily by about 34% over the duration of the test.The abrasive article made in Comparative Example D maintained aconsistent cut rate, as measured by the interval cuts, over the firstfew test intervals, but then decreased abruptly as the sample worethrough the abrasive coating to the backing. The cut rates, as measuredby the interval cuts, of the abrasive articles made in Examples #16 and#18 were similar, but were about half the cut rates, as measured by theinterval cuts, provided by the abrasive articles made in Examples #15and #17.

Particle Crush Strength Values for particles made in Examples #15-#19were measured according to Test Procedure #2. The Crush Strength Valuesreported in Table 11 were the averages of at least 40 particles from agive sample of ceramic aggregate particles.

TABLE 11 Crush Test results for Examples #15-#19 Example Example ExampleExample Example #15 #16 #17 #18 #19 Average 17.4/77.5 22.3/99.27.78/34.6 10.2/45.4  9.7/43.1 Crush Strength Value (lb/N) Standard 2.9/12.9  3.2/14.4 1.85/8.2  2.79/12.4  2.6/11.6 Deviation (lb/N)

Example #20

In Example #20, ceramic aggregate particles were made to demonstratethat the method of the present invention could be used to make ceramicaggregate particles containing grinding aid. Ceramic aggregate precursorslurry was prepared as described in Procedure #1, using grinding aidparticulates (CRY) and non-crystalline ceramic binder precursor (SGP).The particle slurry formulation is listed in Table 12 and was combinedby first combining the ingredients in Table 12 in the order listedexcept for the CRY and SGP. The CRY and SGP were first combined togetherand then slowly added to the remaining ingredients in Table 12.

TABLE 12 Particle slurry formulation for Example #20 Material Quantity(g) TMPTA 300 KB1 3.0 CH 2.0 SGP 400 CRY 1200 Total inorganic solidscontent 84 wt %

Mixing was done in a mixer with a flat beater rotor (obtained fromHobart Corporation, Troy, Ohio, model number Al20T). The CRY/SGP mixturewas added to the resin mixture, and mixing was continued at the slowestmixing speed for about 30 minutes as described in Procedure #2. Thefinal temperature of the mixture was about 100° F. (38° C.). Ceramicaggregate precursor particles were made as described in Procedure #2.The “QUADRO COMIL” was set up with a solid impeller (Arrow 1701), a0.075 inch (1.90 mm) gap, a conical screen with 0.055 inch (1.40 mm)round orifices, and the drive motor was set at 253 rpm. After passingthe slurry through the “QUADRO COMIL” and UV curing system, the at leastpartially-cured ceramic aggregate precursor particles were placed inaluminum pans and thermally-cured in a forced-air oven (obtained fromLindberg/Blue M Company, Watertown, Wis.; model number POM-246F) forabout 6 hours at about 350° F. (177° C.). Precursor particles werescreened using a sieve shaker (obtained from W. S. Tyler, Mentor, Ohio;model number RX 29) and 8 inch (20.3 cm) diameter brass sieves (obtainedfrom W. S. Tyler, Mentor, Ohio). Particles that passed through a #12screen but remained on a #20 screen were collected and prefired asdescribed in Procedure #3. Prefired particles were then reheated to11320° F. (750° C.) as described in Procedure #3. The fired particleswere screened, washed, and dried as described in Procedure #2, and thecrush strength of fired particles was measured as described in TestProcedure #2. The average crush strength of particles in Example #20 was5.3 lbs. (2.4 kg).

Example #21-#22

In Examples #21 and #22, ceramic aggregate particles were made usingnon-crystalline ceramic binder precursor. Example #21 was made withoutcoloring pigment and Example #22 was made with coloring pigment (IO).Ceramic aggregate precursor slurry was prepared as described inProcedure #1. The slurry formulations are listed in Table 13 and werecombined by first combining the ingredients in Table 13 in the orderlisted, except that in Example #22, SGP and IO were first combinedtogether and then slowly added to the remaining ingredients in Table 13.

TABLE 13 Precursor particle slurry formulations for Examples #21 and #22Example 21 Example 22 Material Quantity (g) Quantity (g) TMPTA 693 300KB1 6.9 3.0 CH 4.0 2.0 SCA 28 — SGP 2500 1000 IO — 50 Total inorganic 7777 solids content

Mixing was done in a mixer with a flat beater rotor (obtained fromHobart Corporation, Troy, Ohio: model number A120T). The SGP (Example#21) or SGP/IO mixture (Example #22) were added to each separate resinmixture, and mixing was continued at the slowest mixing speed for about30 minutes as described in Procedure #2. The final temperature of eachmixture was about 100° F. (38° C.). Ceramic aggregate precursorparticles were made as described in Procedure #2. For Example #21, the“QUADRO COMIL” was set up with a solid impeller (Arrow 1701), a 0.075inch (1.90 mm) gap, a conical screen with 0.062 inch (1.57 mm) roundgrater-type orifices, and the drive motor was set at 350 rpm. ForExample #22, the “QUADRO COMIL” was set up with a solid impeller (Arrow1701), a 0.075 inch (1.90 mm) gap, a conical screen with 0.055 inch(1.57 mm) round orifices, and the drive motor was set at 253 rpm. Afterpassing the slurries through the “QUADRO COMIL” and UV curing system,the at least partially-cured ceramic aggregate precursor particles wereplace in aluminum pans and thermally-cured in a forced-air oven(obtained from Lindberg/Blue M Company, Watertown, Wis.; model numberPOM-246F) for about 6 hours at about 350° F. (177° C.). For Example #21,the ceramic aggregate precursor particles were then reduced in size bycausing them to pass through the “QUADRO COMIL” using a solid impeller(Arrow 1701) at a 0.175 inch (4.44 mm) gap and a 0.094 inch (2.39 mm)grater screen. After the reduction in size, the ceramic aggregateprecursor particles for Example #21 were screened using a vibratorygrader (obtained from Exolon Co., Tonawanda, N.Y., model number 501).Particles that passed through a #8 mesh screen but remained on a #24mesh screen were collected and prefired as described in Procedure #2.For Example #22, ceramic aggregate precursor particles were notprocessed further to reduce their size, but were screened using a sieveshaker (obtained from W. S. Tyler, Mentor, Ohio; model number RX 29) and8 inch (20.3 cm) diameter brass sieves (obtained from W. S. Tyler,Mentor, Ohio). Particles that passed through a #12 screen but remainedon a #20 screen were collected and prefired as described in Procedure#2. Ceramic aggregate particles for Examples #21 and #22 were thenreheated to 1382° F. (750° C.) as described in Procedure #2. The firedparticles for each Examples #21 and #22 were screened, washed, and driedas described in Procedure #2, and the crush strength of fired particleswas measured as described in Test Procedure #2. Fired particles fromExample #21 appeared shiny, white, and translucent, and the averagecrush strength was 53.6 lbs. (24.3 kg). Fired particles from Example #22appeared shiny, red, and opaque, and the average crush strength was 44.8lbs. (20.3 kg).

Crush Strength Values for Different Abrasive Grain to Ceramic Bond PhaseRatios

Table 14 is designed to demonstrate the effect of abrasive grain toceramic bond phase ratio on Crush Strength Value. The weight and volumeratios of abrasive grain to ceramic bond phases are listed in Table 14for ceramic aggregate particles of selected examples, along withcorresponding Crush Strength Values measured according to Test Procedure#2.

For glass-bonded ceramic aggregate particles (i.e., Examples #1, #2, #3,and #8) the actual volume ratio of abrasive grains to glass bond phasewas determined as follows: ceramic aggregate particles for each givenexample were dried for about 2 hours at about 100° C. in a forced-airoven (obtained from Despach Industries, Minneapolis, Minn.; model numberALD2-11) in order to remove moisture from the surface of the particles.Then, the Total Volume of about 10 grams of particles for each givenexample was measured by helium pycnometry using a “ACCU PYC 1330”(obtained from Micromeritics Inc., Norcorss, Ga., under the tradedesignation “ACCU PYC 1330”). For each of Examples #1, #2, #3, and #8the ceramic aggregate particles were soaked in 30% hydrofluoric acid forabout 2 hours which dissolved the glass bond phase but not the abrasivegrains. The hydrofluoric acid solution was decanted and the abrasivegrains removed. The abrasive grains were washed with deionized water anddried for about 2 hours at about 100° C. in the forced-air oven(obtained from Despach Industries, Minneapolis, Minn.; model numberALD2-11) to remove moisture. The volume of the remaining abrasive grainswas measured by helium pycnometry using the “ACCU PYC 1330.” The volumeratios and percentages of abrasive grain to glass bond phase werecalculated and listed in Table 14. For the alumina-bonded ceramicaggregate particles (i.e., Examples #16 and #18), volume ratios wereestimated from the weight fractions of abrasive grain and alumina bondphases assuming nominal material densities of 4.00 g/cc for both theabrasive grain and alumina bond phases. These data are summarized inTable 14.

TABLE 14 Crush Strength Values for Different Abrasive Grain to CeramicBond Phase Ratios Example Particles Percent Sample, Ratio - AbrasiveAbrasive Grain Average abrasive Grain:Bond By By Crush grade Bond By Byweight volume Strength and type Type weight volume (wt %) (vol %) (lb)Example #1 Glass 3.0:1 1.62:1 75.0 61.8 25.7 #100 AG321 Example #2 Glass1.5:1 0.81:1 60.0 44.7 >>60 #60 AG321 Example #3 Glass 3.0:1 1.62:1 75.061.8 44.0 #60 AG321 Example #8 Glass 2.5:1 1.16:1 71.4 53.7 41.3#60/P320 AG321 Example #16 REO- 2.5:1 2.5:1 71.4 71.4 22.3 #60/P320alumina AG321 Example #18 REO- 2.5:1 2.5:1 71.4 71.4 10.2 P80 AO alumina

Table 14 illustrates that higher ceramic binder content results inhigher particle strength.

We claim:
 1. A method of making abrasive aggregate particles, the methodcomprising: forming a composition comprising (1) curable binderprecursor material, (2) ceramic binder precursor material, and (3) aplurality of abrasive particulates into ceramic aggregate precursorparticles by forcing the composition through at least one orifice in asubstrate; at least partially curing the ceramic aggregate precursorparticles; separating the aggregate precursor particles from thesubstrate; and heating the ceramic aggregate precursor particles toprovide abrasive aggregate particles wherein the abrasive particulatesarc bonded together by the ceramic binder.
 2. A method according toclaim 1, wherein the at least partially curing the ceramic aggregateprecursor particles comprises at least partially thermally curing theceramic aggregate precursor particles.
 3. A method according to claim 1,wherein the at least partially curing the ceramic aggregate precursorparticles comprises at least partially radiation curing the ceramicaggregate precursor particles.
 4. A method according to claim 3, whereinfirst ceramic aggregate precursor particles are at least partially curedto provide second ceramic aggregate precursor particles comprising (i)curable binder precursor material, (ii) ceramic binder precursormaterial, (iii) a plurality of abrasive particulates, and (iv) reactionproduct of at least partially radiation curing the first ceramicaggregate precursor particles; the method further comprises at leastpartially curing the second ceramic aggregate precursor particles.
 5. Amethod according to claim 3, wherein the at least partially radiationcuring the ceramic aggregate precursor particles is provided by aradiation energy source selected from the group consisting of electronbeam, ultraviolet light, visible light, microwave, laser light andcombinations thereof.
 6. A method according to claim 1, wherein theheating the ceramic aggregate precursor particles is conducted at atemperature in the range from about 500° C. to about 1500° C.
 7. Amethod according to claim 3, wherein the composition further comprisesphotoinitiator.
 8. A method according to claim 3, wherein the curablebinder precursor material comprises at least one of epoxy resin,acrylated urethane resin, acrylated epoxy resin, ethylenicallyunsaturated resin, aminoplast resin having at least one pendantunsaturated carbonyl group, isocyanurate derivative having at least onependant acrylate group, isocyanate derivative having at least onependant acrylate group, or combinations thereof.
 9. A method accordingto claim 3, wherein the curable binder precursor material comprisesvinyl ether.
 10. A method according to claim 3, wherein the compositionis essentially free of solvent.
 11. A method according to claim 1,wherein the abrasive particulates are selected from the group consistingof fused aluminum oxide, ceramic aluminum oxide, white fused aluminumoxide, heat treated aluminumn oxide, silica, silicon carbide, greensilicon carbide, alumina zirconia, diamond, ceria, cubic boron nitride,garnet, tripoli, and combinations thereof.
 12. A method according toclaim 1, wherein the composition further comprises solid particulatesselected from the group consisting of fillers, grinding aids, fibers,electrically active particulates, pigments, and combination thereof. 13.A method according to claim 12, wherein the plurality of solidparticulates have an average particle size in the range from 0.5 to 1500micrometers.
 14. A method according to claim 1, wherein the compositionis formed into ceramic aggregate precursor particles by at least one ofextruding, milling, or calandering.
 15. A method according to claim 1,wherein, after at least partially curing, the ceramic aggregateprecursor particles have an average particle size and the method furthercomprises reducing the average particle size of the ceramic aggregateprecursor particles using at least one of milling, crushing or tumbling.16. A method according to claim 1, wherein, after heating, the abrasiveaggregate particles have an average particle size and the method furthercomprises reducing the average particle size of the abrasive aggregateparticles using at least one of milling, crushing or tumbling.
 17. Amethod according to claim 1, wherein the ceramic binder precursormaterial comprises crystalline or non-crystalline ceramic material. 18.A method according to claim 1, wherein the ceramic binder precursormaterial is selected from the group consisting of glass powder, frits,clay, fluxing minerals, silica sols, sinterable ceramic powders andcombinations thereof.
 19. A method according to claim 1, wherein atleast a portion of the abrasive aggregate particles are rod-shaped. 20.A method of making abrasive aggregate particles, the method comprising:forming a composition comprising (1) curable hinder precursor material,(2) ceramic binder precursor material, and (3) a plurality of abrasiveparticulates into ceramic aggregate precursor particles by forcing thecomposition through at least one orifice in a substrate; separating theceramic aggregate precursor particles from the substrate; at leastpartially curing the ceramic aggregate precursor particles; at leastpartially coating the ceramic aggregate precursor particles withmetal-oxide particulate; and heating the ceramic aggregate precursorparticles to provide abrasive aggregate particles wherein the abrasiveparticulates are bonded together by the ceramic binder.
 21. A method ofmaking an abrasive article, the method comprising: forming a compositioncomprising (1) curable binder precursor material, (2) ceramic binderprecursor material, and (3) a plurality of abrasive particulates intoceramic aggregate precursor particles by forcing the composition throughat least one orifice in a substrate; separating the ceramic aggregateprecursor particles from the substrate; at least partially curing theceramic aggregate precursor particles; heating the ceramic aggregateprecursor particles to provide abrasive aggregate particles wherein theabrasive particulates are bonded together by the ceramic binder; andcombining at least a portion of the ceramic aggregate particles withabrasive article binder material to provide an abrasive article.
 22. Amethod according to claim 21, wherein the abrasive article is a nonwovenabrasive article and at least a portion of the ceramic aggregateparticles are rod-shaped.